Surface light source, method for manufacturing the same and apparatus using it

ABSTRACT

The light emitted from a spot light source ( 45 ) is emitted at a linearly extending region by a wedge-like light conductor ( 47 ) and deflected by a prism sheet ( 50 ). This light is emitted in a direction perpendicular to a light incident surface ( 44   a ) of the light conductor plate ( 44 ) and has a directivity narrow in a widthwise direction of the light conductor plate ( 44 ). The light conductor plate ( 44 ) is formed, at its bottom surface, with a multiplicity of diffusion patterns ( 46 ) in a rectangular triangular form. The light reflected upon the diffusion pattern ( 46 ) is emitted perpendicularly to a light emitting surface ( 44   b ) of the light conductor plate ( 44 ). At this time, part of the light incident on the diffusion pattern ( 46 ) transmits through the diffusion pattern ( 46 ) whereby the directivity of emission light is narrowed in a lengthwise direction of the light conductor plate.

TECHNICAL FIELD

[0001] The present invention relates to a surface light source deviceand manufacturing method for the same and apparatus using the samedevice. More particularly, it relates to a surface light source devicefor use as a backlight or front light of a liquid crystal display unitor the like and manufacturing method for the same.

BACKGROUND OF THE INVENTION

[0002] The backlight or front light having a light-emitting diode (LED),as a light source, has the features of size-reduced light source, longlife, high performance, unnecessary exclusive power source and so on,and in many cases is used as a light of a liquid crystal display unitused in a display of a portable apparatus. Of among these features, twopoints, i.e. high efficiency and small size, are particularly important.This is because the surface light source device, if high in efficiencyincreases the brightness on a light-emitting surface of the surfacelight source device, making easy to view an image on the liquid crystaldisplay unit. Furthermore, with high efficiency, the surface lightsource device is decreased in consumption power and increased in batterylife. Meanwhile, the portable apparatus cannot be size-reduced withoutthe size reduction of the surface light source device. This requiresreducing the area of a non-emitting region and the thickness as well.

[0003] Also, in the case of using as a display of a portable apparatus,it is satisfactory to view the display at a front thereof. There is lessneed to view in an oblique direction. In many cases, it is ratherpreferred not to be seen obliquely. Accordingly, a broad directivitycharacteristic is not required for the light to be emitted from thesurface light source device. In order to improve the efficiency of thesurface light source device, it is preferred to emit light only in adirection having a certain degree of spread, in a direction of a normalline given on a light emitting surface of the surface light sourcedevice.

[0004] Now, in FIGS. 1 and 2 is shown an explosive perspective view andsectional view of a surface light source device of a general structure.The surface light source device 1, for use as a backlight, is structuredwith a light conductor plate 2 for light confinement, a light emittingpart 3 and a reflection plate 4. The light conductor plate 2 is formedof a transparent resin having a high refractive index, such as apolycarbonate resin or a methacrylic resin. The light conductor plate 2has, in a lower surface, diffusion patterns 5 formed by concavo-convexworking, dot printing with a diffuse-reflection ink or the like. Thelight emitting part 3 has a plurality of light-emitting diodes 7 mountedon a circuit board 6, and opposed to a side surface (light incidentsurface 2 a) of the light conductor plate 2. The reflection plate 4,formed by a white-resin sheet, is bonded at both sides onto a lowersurface of the light conductor plate 2 by double-sided tapes 8.

[0005] In the surface light source device 1 like this, the light,emitted from the light emitting part 3 and guided at a light incidentsurface 2 a into the light conductor plate 2, travels while repeatingregular reflections at between the upper surface (light emitting surface2 b) and the lower surface of the light conductor plate 2 as shown inFIG. 2. Upon incidence on the diffusion pattern 5, diffuse-reflectionoccurs. In case the incidence is at an angle smaller than a criticalangle of total reflection toward the light emitting surface 2 b, thelight is emitted at the light emitting surface 2 b to the outside.Meanwhile, the light, passed a point where there is no diffusion pattern5 on the lower surface of the light conductor plate 2, is reflected bythe reflection plate 4 to return again into the light conductor plate 2,preventing light amount loss at the lower surface of the light conductorplate 2.

[0006] However, although the surface light source device 1 having such astructure is simple in structure, it is structurally worse in lightutilization efficiency. It has been impossible to emit onlyapproximately 20% of the emission light of from the light-emitting diode7, at the light emitting surface 2 b of the light conductor plate 2.

[0007] Furthermore, in the surface light source device 1 in such astructure, in order to direct the light emitted in a directionapproximate to the parallel with the light emitting surface 2 b of thelight conductor plate 2 toward a direction perpendicular to the lightemitting surface 2 b, a diffusion plate 9 is used superposed on thelight conductor plate 2 as shown in FIG. 3. The surface light sourcedevice 1 has an increased thickness, making it difficult to size-reducethe surface light source device 1. Moreover, where using a diffusionplate 9, the light passed the diffusion plate 9 turns into a Lambertianlight. Because of broad directivity characteristic, the brightness atthe front is low, thus. lowering the utilization efficiency of light.

[0008] Meanwhile, the surface light source device 1 structured as shownin FIG. 1 uses a light emitting part 3 mounted with a plurality oflight-emitting diodes 7. Thus, it is difficult to size-reduce the lightemitting part 3. Also, the power consumption of the surface light sourcedevice 1 cannot be reduced.

[0009] On the other hand, the surface light source device usinglight-emitting diodes is used on the commodities having a strongrequirement of portability, such as cellular phones and PDAs, because ofits reduced size and weight. There is a strong need for the lifeincrease of the power source in view of improved portability. Thereduction of power consumption is strongly desired for the surface lightsource device for use in the same. For this reason, there is advancementof decreasing the number of light-emitting diodes to be used.

[0010] Under this situation, there is a proposal of a surface lightsource device 11 as in FIG. 4 using one light-emitting diode(JP-A-11-231320). In this surface light source device 11, a lightemitting part 12 is made by arranging a light-emitting diode 14 opposedto an end of a wedge-formed bar member 13, to arrange the light emittingpart 12 opposed to a light incident surface 15 a of a light conductorplate 15. The light conductor plate 15 also is in a wedge form to have,on its lower surface, a diffuse-reflection sheet 17 to diffuse-reflectthe leak light at the lower surface of the light conductor plate 15 andreturn it into the light conductor plate 15. Opposed to a light emittingsurface 15 b of the light conductor plate 15, superposed are a diffusionplate 18 and the prism sheet 19. Also, a prism-formed pattern 16 isformed on the light incident surface 15 a of the light conductor plate15.

[0011] According to the surface light source device 1 like this, thelight utilization efficiency of a light source is improved because ofthe capability of driving with one light-emitting diode 14. However,because light diffusion is done by the diffuse-reflection sheet 17 anddiffusion plate 18, directivity is broadened as shown in FIG. 5. Due tothe lower in directivity characteristic, the efficiency is notsufficient as the entire of the surface light source device 11.Furthermore, because the diffusion plate 18 and prism sheet 19 aresuperposed on the light conductor plate 15, the surface light sourcedevice 1 is increased in thickness. The light source 12 issize-increased by the bar-formed member 13. Thus, there has beendifficulty in reducing the size.

[0012] Also, there is a showing in FIG. 6 as another surface lightsource device 21 using one light-emitting diode. This has onelight-emitting diode 23 arranged opposed to a center of a light incidentsurface 22 a of the light conductor plate 22, to concentrically arrangeU-shaped diffusion patterns 24 about the light-emitting diode 23 in alower surface of the light conductor plate 22. Each diffusion pattern 24extends in a direction orthogonal to a direction connected to thelight-emitting diode 23.

[0013] Then, in this surface light source device 21, the light emittedfrom the light-emitting diode 23 enters at the light incident surface 22a the light conductor plate 22 to travel within the light conductorplate 22. Within the light conductor plate 22, the light striking thediffusion pattern 24 is reflected upon an interface of the diffusionpattern 24 as shown in FIG. 7 and emitted toward the light emittingsurface 22 b in a surface of the light emitting surface 22 b. Only thelight incident, at an incident angle smaller than a critical angle oftotal reflection, on the light emitting surface 22 b is allowed to emitat the light emitting surface 22 b to the outside.

[0014] However, the diffusion pattern 24 is circumferentially uniformabout the light source. The light if striking the diffusion pattern 24,in plan view, is not changed in traveling direction. There is nodiffusion action of light in the circumferential direction about thelight source. Consequently, the evenness of light in the circumferentialdirection is determined depending solely on the circumferentialdistribution of light amount of the light source or the distribution ofamount of the light entered at the light incident surface into the lightconductor plate.

[0015] As a result of this, the circumferential directivitycharacteristic is narrow in this surface light source device 21, thedirectivity of the light emitted from the light conductor plate 22 isextremely narrow in a widthwise direction of the light conductor plate22 but broad in a lengthwise direction as shown in FIG. 8. For thisreason, a diffusion plate for moderating the widthwise directivity isessentially required, increasing the thickness of the surface lightsource device 21. Meanwhile, because the diffusion plate causesdiffusion not only in the widthwise direction but also in the lengthwisedirection, the lengthwise directivity is extremely worsened and hencethe brightness in the perpendicular direction is lowered.

[0016] Next, in FIG. 9 is shown a surface light source device 31 for useas a front light. In this surface light source device 31, a plurality ofslits 33 are formed of a material different from the light conductorplate 32 or air on an upper surface of the light conductor plate 32. Alinear light source 34 just like a cold-cathode tube is arranged opposedto a side surface of the light conductor plate 32. Consequently, thelight, exited from the linear light source 34 to be incident on thelight conductor plate 32, is totally reflected upon the slits 33 andemits at a lower surface of the light conductor plate 32. This isreturned to the light conductor plate 32 by the reflection upon areflective-type liquid crystal display panel 35, to pass through betweenthe slits 33 and emit at the upper surface of the light conductor plate32.

[0017] However, in the surface light source device 31 like this, becausesufficiently many slits 33 cannot be provided, the utilizationefficiency of light is low. Also, because the slits 33 must be formed inthe interior of the light conductor plate 32, there has been adifficulty of manufacture.

[0018] Similarly, there is a proposal of a surface light source devicefor front light having a plurality of island regions formed different inrefractivity index from the other within the light conductor plate(JP-A-7-199184). This is also insufficient in light utilizationefficiency, and the manufacture is difficult.

[0019] Meanwhile, the other surface light source devices for front lightinclude the use of a light conductor plate gradually, stepwise reducedin thickness as distant from the light source (JP-A-10-326515), theprovision of a prism sheet on a lower surface of a wedge-formedconductor plate (JP-A-10-301109), the forming with a concavo-convexpattern sectionally in rectangular in a lower surface of a lightconductor plate (JP-A-10-123518), and the provision with V-formed groovestrips in an upper surface of a wedge-formed conductor plate(JP-A-11-64641).

[0020] In the surface light source device like this, despite having arelatively simplified structure, the utilization efficiency of light isstill insufficient thus darkening the screen.

DISCLOSURE OF THE INVENTION

[0021] It is a first object of the present invention to provide asurface light source device excellent in directivity characteristic,manufacturing method for the same and apparatus using the same device.

[0022] A second object of the present invention is to provide a surfacelight source device excellent in light utilization efficiency,manufacturing method for the same and apparatus using the same device.

[0023] A first surface light source device according to the presentinvention is in a surface light source device having a light source anda light conductor plate for spreading the light introduced from thelight source to nearly entire of a light emitting surface and emittingit from the light emitting surface, the surface light source devicecharacterized in that: 50% or more of the light emitted from the lightconductor plate is emitted within an area defined by angles of emissionof up to 30 degrees as measured in a direction perpendicular to thelight emitting surface of the light conductor plate. Herein, the area ofwithin a predetermined angle as measured in a certain direction refersto an area within a cone where an axis inclining a predetermined anglewith respect to a certain direction about a certain direction rotatesabout the same direction, instead of a region within a predeterminedangle on one side with respect to a certain direction. Also, a certainangle as viewed in a certain direction refers merely to an angle definedwith respect to a certain direction.

[0024] According to an experiment, it has been found that the lightemitted outward of 30 degrees with respect to a direction perpendicularto a screen of an image display unit results in loss thus loweringvisibility on the image display unit. Accordingly, by collecting themajor part of the light amount emitted from the surface light sourcedevice to within 30 degrees with respect to a direction perpendicular toa light emitting surface, even where this is used for an image displayunit, collection is possible to within 30 degrees with respect to adirection perpendicular to the screen, making favorable the visibilityon the image display unit. The invention, without placing a prism sheetor the like on the light emitting surface, can emit 50% or more of thelight emitted from the light conductor plate is emitted within an areadefined by angles of emission of up to 30 degrees as measured in adirection perpendicular to the light emitting surface of the lightconductor plate.

[0025] A second surface light source device according to the inventionis in a surface light source device for lighting a reflective-typedisplay device having a light source and a light conductor plate forspreading the light introduced from the light source to nearly entire ofa light emitting surface and emitting it from the light emittingsurface, the surface light source device characterized in that: 50% ormore of the light emitted from the light conductor plate to thereflective-type display unit is emitted to an area defined by angles ofwithin the half-width of a reflection light intensity-angle distributionon the reflective-type display device as measured in a directionperpendicular to the light emitting surface of the light conductorplate. Herein, a width at half maximum refers to an angle in a half of afull-width at half maximum.

[0026] Where structuring a reflective-type liquid crystal display unitby a reflective-type display device and a surface light source device,in case the directivity characteristic of the surface light sourcedevice is broadened, the reflection-light intensity angularcharacteristic of the surface light source device is graduallymoderated. When the directivity characteristic of the surface lightsource device is broadened greater than the reflection-light angularcharacteristic of the image display panel, there was a lower in theintensity of a perpendicular component of the light reflected upon theimage display panel. Accordingly, in the second surface light sourcedevice, the range in which, of the light amount emitted from the lightconductor plate, 50% or more is emitted is provided narrower than afull-width at half maximum of a reflection light intensity-angledistribution of the reflective-type display device. Thus, thedirectivity characteristic of the surface light source device is madenarrower than a reflection-light angular characteristic of the imagedisplay panel, making possible to enhance a front intensity of the imagedisplay unit.

[0027] A third surface light source device according to the invention isin a surface light source device having a light source and a lightconductor plate nearly in a rectangular form for spreading the lightintroduced from the light source to nearly entire of a light emittingsurface and emitting it from the light emitting surface, the surfacelight source device characterized in that: 50% or more of the lightemitted from the light conductor plate is emitted to an area having abrightness of a half or greater of a maximum brightness value of theemission light, the area seen in both a longer-side direction and ashorter-side direction has an angle width of 30 to 70 degrees.

[0028] In a surface light source device using a light conductor platenearly in a rectangular form, in case the major part of emission lightis concentrated to a region having a brightness of a half or greater ofa maximum brightness wherein the angular width (total width) is given30-70 degrees, it is possible to obtain a preferable directivitycharacteristic despite not to be considered as an ideal directivitycharacteristic.

[0029] A fourth surface light source device according to the inventionis in a surface light source device having a light source and a lightconductor plate for spreading the light introduced from the light sourceto nearly entire of a light emitting surface and emitting it from thelight emitting surface, the surface light source device characterized inthat: the brightness of the light emitted from the light conductor plateperpendicularly is lower than that of the light emitted to an areaaround thereof.

[0030] In the fourth surface light source device, particularly thesurface light source device for use on a reflective-type image displayunit, the noise light caused by light leak from the surface light sourcedevice is susceptible to the effect of a directivity characteristic ofthe light emitted from the surface light source device whereas the light(image) returning due to the reflection upon the image display device isless changed by a change in a directivity characteristic of the surfacelight source device due to a diffusion characteristic of the imagedisplay device. Consequently, in case the directivity characteristic ofthe surface light source device is made lower in brightness than thesurrounding in a direction of a perpendicular given on the lightemitting surface, noise light can be reduced in a front direction andimage visibility can be improved.

[0031] A fifth surface light source device according to the invention isin a surface light source device having a light source and a lightconductor plate for spreading the light introduced from the light sourceto nearly entire of a light emitting surface and emitting it from thelight emitting surface, the surface light source device characterized inthat: a direction in which emission light brightness is maximum in aperipheral region of the light conductor plate is inclined to adirection of a center of the light conductor plate as compared to adirection in which emission light brightness is maximum in a centralarea of the light conductor plate.

[0032] By changing the orientation that is maximum in emission lightbrightness depending upon a position of the light conductor plate as inthe fifth surface light source device, a lens action can be provided toreduce the unevenness of in-plane brightness of the surface light sourcedevice. This is possible, for example, by making somewhat different,from position to position, the form of diffusion pattern having adeflecting slant angle and light re-incident angle provided in a backsurface of the surface light source device. This can provide thediffusion pattern with a lens action.

[0033] A sixth surface light source device according to the invention isin a surface light source device having a light conductor plate forspreading the introduced light to nearly entire of a light emittingsurface and emitting it from the light emitting surface, a light sourcesmaller in size as compared to a light incident surface of the lightconductor plate, luminous flux shaping means for spreading the lightemitted from the light source to nearly entire of the light incidentsurface and emitting it, the surface light source device characterizedin that: 50% or more of the incident light on the light conductor plateis included in an area defined by angles of 26 degrees as viewed from adirection perpendicular to the light emitting surface of the lightconductor plate.

[0034] In this sixth surface light source device, the luminous fluxshaping means is used to broaden the light emitted from a small lightsource in a lengthwise direction of the luminous flux shaping means andcollect the major part of the light amount incident on the lightconductor plate to within 26 degrees as viewed in a directionperpendicular to the light emitting surface. Consequently, for also thelight emitted from the light emitting surface of the light conductorplate, obtained is a high directivity of within 40 degrees in alengthwise direction of the light incident surface of the lightconductor plate.

[0035] In an embodiment of a sixth surface light source device accordingto the invention, two-thirds or more of the total light emitted from theluminous flux shaping means is emitted to an area defined by angles ofup to 40 degrees from a lengthwise direction of a light emitting surfaceof the luminous flux shaping means as viewed in a directionperpendicular to the light emitting surface of the light conductorplate, the luminous flux shaping means having, at a light emittingsurface side, means to deflect the light emitted from the luminous fluxshaping means to a direction perpendicular to a light emitting surfaceof the luminous flux shaping means.

[0036] The present embodiment concerning the sixth surface light sourcedevice concentrates the major part of the light amount emitted from theluminous flux shaping means into a narrow range of within 40 degreeswith respect to a lengthwise direction of the light emitting surface ofthe luminous flux shaping means, and causes this to emit in aperpendicular direction by the deflecting means. Accordingly, it ispossible to introduce a high directivity light aligned in direction in alengthwise direction of the luminous flux shaping means into the lightconductor plate. Ultimately, the light emitted at the light emittingsurface of the light conductor plate has a directivity narrowed in adirection corresponding to the lengthwise direction of the luminous fluxshaping means. In a different embodiment of a sixth surface light sourcedevice according to the invention, the luminous flux shaping means isformed of a transparent material. A regular reflection plate may beprovided opposed to the opposite side of the light emitting surface.

[0037] Because the present embodiment concerning the sixth surface lightsource device has a reflection plate provided on an opposite surface(back surface) to the light emitting surface of the luminous fluxshaping means, the light leaked at the back surface of the luminous fluxshaping means can be reflected by the reflection plate to be re-incidentupon the interior of the luminous flux shaping means, thus enhancinglight utilization efficiency and raising the brightness on the surfacelight source device. Moreover, because the reflection plate uses aregular reflection plate, there is no possibility of disturbing thedirection of the light emitted from the luminous flux shaping means bythe light leaked from the luminous flux shaping means and reflected bythe regular reflection plate to be re-incident. The light emitted fromand deflected by the luminous flux shaping means can be narrowed indirectivity characteristic. Incidentally, the luminous flux shapingmeans like this can use, for example, a transparent resin having a highrefractive index formed non-parallel at between a light emitting surfaceand a back surface thereof.

[0038] A seventh surface light source device according to the inventionis in a surface light source device having a plurality of relativelysmall light sources arranged with a spacing, means for decreasing adirectivity of the light emitted from the light sources in a directionthat the light sources are arranged, and a light conductor plate forspreading the light introduced from the light sources to nearly entireof a light emitting surface and emitting it from the light emittingsurface, the surface light source device characterized in that: 50% ormore of the incident light on the light conductor plate is included inan area defined by angles of 26 degrees as viewed from a directionperpendicular to the light emitting surface of the light conductorplate.

[0039] Because the seventh surface light source device causes the majorpart of the light amount incident on the light conductor plate to beincident on an area of within 26 degrees as viewed in a directionperpendicular to the light emitting surface, the light, to be emitted atthe light emitting surface of the light conductor plate, in its majorpart is emitted into an area of nearly 40 degrees in a direction thatthe spot light sources are arranged. Meanwhile, the light emitted fromthe plurality of small light sources arranged at an interval has adirectivity narrowed, before incidence on the light conductor plate, inthe light source arranging direction. Consequently, within the lightconductor plate, the directivity may be narrowed only in a thicknessdirection of the light conductor plate. Accordingly, within the lightconductor plate, the directivity is aligned in one direction thusfacilitating to control light and raising the controllability of thelight to be emitted at the light emitting surface of the light conductorplate. Also, the light to be incident on the light conductor plate has adirectivity narrowed in one direction. Because in this direction thereis no necessity to raise the directivity of the light by the lightconductor plate, the light conductor plate can be easily reduced inthickness.

[0040] In an embodiment of the sixth or seventh surface light sourcedevice according to the invention, in the area, 50% or more of theincident light on the light conductor plate may not be concentrated inan area defined by angles of up to 10 degrees in every direction.

[0041] In the present embodiment of the sixth or seventh surface lightsource device, because the major part of the light amount incident onthe light conductor plate does not concentrate into a narrow range ofwithin 10 degrees in any direction, by merely, somewhat moving a line ofsight, light reaches and does not reach the eye and hence flicker lessoccurs.

[0042] In a different embodiment of a sixth or seventh surface lightsource device according to the invention, at least one of the lightemitting surface and the opposite surface of the light conductor plateis provided with a concavo-convex formed pattern having a deflectingslant surface which is slanted so that a normal line directed inside ofthe light conductor plate inclines to a direction that the light sourceis arranged, a direction of the normal line and a direction of light'straveling within the light conductor plate being in parallel as viewedin a direction perpendicular to the light emitting surface of the lightconductor plate.

[0043] In the present embodiment concerning the sixth or seventh surfacelight source device, formed is a concavo-convex pattern having adeflecting slant surface slanted such that a normal line directed towardthe inside of the light conductor plate inclines toward a directionarranging the light sources. Because the direction of the normal lineand direction of light's traveling within the light conductor plate arein parallel as viewed in a direction perpendicular to the light emittingsurface of the light conductor plate, part of the light incident on thedeflecting slant surface as viewed in a direction perpendicular to thedirection of light's traveling is totally reflected upon the deflectingslant surface and emitted at the light emitting surface, while theremaining light transmits through the deflecting slant surface. As aresult of this, of the light incident on the deflecting slant surface,only the light incident at a particular angle is allowed to emit at thelight emitting surface. As viewed in this direction, the light emittedat the light emitting surface is narrowed in its directivity.

[0044] In a further different embodiment of a sixth or seventh surfacelight source device according to the invention, of a total light amountemitted to a plane including a direction of light's traveling within thelight conductor plate and perpendicular to the light emitting surface ofthe light conductor plate, two-thirds or more of the light being emittedto an area defined by angles of up to 40 degrees with respect to thelight emitting surface of the light conductor plate, the light conductorplate having, at a light emitting surface side, means to deflect thelight emitted from the light emitting surface to a directionperpendicular to the light emitting surface.

[0045] In the present embodiment concerning the sixth or seventh surface light source device, the major part of the light of within the lightconductor plate is concentrated into a narrow range of 40 degrees withrespect to the light emitting surface of the light conductor plate. Thisis emitted in a perpendicular direction by the deflecting means.Consequently, it is possible to emit a light high in directivity alignedin direction at the light emitting surface of the light conductor plate.Furthermore, with the deflecting means, it is possible to narrow thedirectivity of the light to be emitted at the light emitting surface ofthe light conductor plate.

[0046] In a further different embodiment of a sixth or seventh surfacelight source device according to the invention, the angle defined by anormal line direction of the deflecting slant surface and a directionperpendicular to the light emitting surface of the light conductor plateis 10 degrees or smaller, a regular reflection plate being provided onthe opposite side of the light emitting surface of the light conductorplate.

[0047] According to the present embodiment concerning the sixth orseventh surface light source device, the angle defined by a normal linedirection of the deflecting slant surface and a direction perpendicularto the light emitting surface of the light conductor plate is 10 degreesor smaller. The light extracted at the light emitting surface when anincident light is smaller than a critical angle of total reflection dueto the total reflection at between the light emitting surface and theopposite surface can be obtained aligned to a narrow angle. Inparticular, in case the angle defined between a normal-line direction onthe deflecting slant surface and a direction perpendicular to the lightemitting surface of the light conductor plate is made 10 degrees orsmaller, light emission is possible to a narrow range of approximately?20 degrees. In this manner, the light emitted nearly parallel with thelight emitting surface of the light conductor plate can be directed to adirection perpendicular to the light emitting surface by the lightdeflecting means arranged, for example, opposite to the light emittingsurface of the light conductor plate.

[0048] An eighth surface light source device according to the inventionis in a surface light source device having a light source and a lightconductor plate for spreading the light introduced from the light sourceto nearly entire of a light emitting surface and emitting it from thelight emitting surface, the surface light source device characterized inthat: the light conductor plate having a plurality of deflecting slantsurfaces to totally reflect a light traveling in the light conductorplate and emitting it from a light emitting surface; as viewed in adirection perpendicular to the light emitting surface of the lightconductor plate, a direction of light's traveling within the lightconductor plate being aligned nearly in one direction at each position,and a normal line direction of the deflecting slant surface beingdistributed within 30 degrees about a direction of light's traveling;and the deflecting slant surface in a plane including a direction oflight's traveling within the light conductor plate and perpendicular tothe light emitting surface having a section of a straight line.

[0049] According to the eighth surface light source device, because thelight conductor plate has a plurality of deflecting slant surfaces tototally reflect the light traveling in the light conductor plate andemit it at the light emitting surface, by transmitting the lightincident on the deflecting slant surface at an incident angle smallerthan the total reflection angle, the directivity of the emission lightcan be narrowed as viewed in a direction perpendicular to a section ofthe deflecting slant surface. On the other hand, as viewed in adirection perpendicular to the light emitting surface of the lightconductor plate, the direction of light's traveling of within the lightconductor plate is aligned nearly in one direction at each position andthe normal-line direction on the deflecting slant surface is distributedabout the direction of light's traveling. Accordingly, the directivityangle can be broadened by totally reflecting on the deflecting slantsurface the light having an extremely narrow directivity angle as viewedfrom the light emitting surface. Consequently, it is possible. to emitat a proper directivity angle the light having an excessively widedirectivity angle in a direction perpendicular to the light incidentsurface of the light conductor plate but an excessively narrowdirectivity angle in a direction parallel with the light incidentsurface of the light conductor plate. Thus, light loss can be reduced asless as possible to improve front brightness. In particular, bydistributing the deflecting slant surfaces within an angle of within 30degrees as viewed from the light emitting surface, the light to beemitted at the light emitting surface of the light conductor plate canbe broadened to approximately ±45 degrees.

[0050] A ninth surface light source device according to the invention isin a surface light source device having a light source and a lightconductor plate for spreading the light introduced from the light sourceto nearly entire of a light emitting surface and emitting it from thelight emitting surface, the surface light source device characterized inthat: at least one of the light emitting surface of the light conductorplate and the opposite surface is provided with concave-formed patternsin plurality structured with a deflecting slant surface for totalreflection of light and a light re-incident surface for re-incidence ofthe light transmitted through the deflecting slant surface; theconcave-formed pattern having a section in a triangular groove formhaving a deflecting slant surface and a light re-incident surface, and asection nearly uniform in a direction perpendicular to a direction oflight's traveling within the light conductor plate, the deflecting slantsurface having an inclination of 45-65 degrees relative to a surfacehaving the concave-formed patterns; and as viewed in a directionperpendicular to a plane including a direction of light s travelingwithin the light conductor plate and perpendicular to the light emittingsurface of the light conductor plate, 50% or more of the light emittedfrom the light emitting surface of the light conductor plate beingincluded in a range of within 30 degrees as viewed from the lightemitting surface.

[0051] In the ninth surface light source device, because formed inplurality the concave-formed patterns structured with a deflecting slantsurface to totally reflect light and a light re-incident surface for thelight transmitted through the deflecting slant surface to bere-incident, the light traveling in the light conductor plate can beemitted at the light emitting surface of the light conductor plate bytotal reflection upon the deflecting slant surface. Meanwhile, becausethe light transmitted through the deflecting slant surface returns atthe light re-incident surface into the light conductor plate, there isless possibility that the light transmitted through the deflecting slantsurface results in loss. Thus, the light utilization efficiency can beenhanced to increase the brightness on the surface light source device.Furthermore, in case the surface having the concave-formed patterns isprovided with an inclination of 45-60 degrees, the major part of thelight amount to be emitted at the light emitting surface of the lightconductor plate can be emitted to a narrow range of within 30 degrees asmeasured from the light emitting surface. Accordingly, in case this isdeflected to a direction perpendicular to the light emitting surface byproper deflecting means, it is possible to obtain a narrow directivityof within 30 degrees in that direction.

[0052] In an embodiment concerning a first to sixth, eighth or ninthsurface light source device according to the invention, a relativelysmall light source is arranged at an end on a side of a shorter side ofthe light conductor plate nearly in a rectangular form, a light emittingsurface of the light source being directed to a corner positioned in adiagonal direction of the light conductor plate.

[0053] According to the present embodiment concerning the first tosixth, eighth or ninth surface light source device, it is easy for lightto reach a corner diagonally opposed to a light-conductor-plate cornerin the vicinity of the arrangement of the light source, thus raisingbrightness at this corner.

[0054] A tenth surface light source device according to the invention isin a surface light source device having a light source and a lightconductor plate nearly in a rectangular form for spreading the lightintroduced from the light source to nearly entire of a light emittingsurface and emitting it from the light emitting surface, the surfacelight source device characterized in that: a relatively small lightsource is arranged at an end on a side of a shorter side of the lightconductor plate, a shorter side of the light conductor plate arrangedwith the light source and a longer side of the light conductor platepositioned on a side close to the light source having parts incliningrelative to the respective opposed shorter side and longer side.

[0055] According to the tenth surface light source device, the shorterside of the light conductor plate where the light source is arranged andthe longer side of the light conductor plate positioned on a side closeto the light source are inclined relative to the respective opposedshorter side and longer side. Consequently, by properly selecting aninclination angle of the inclining part, the light emitted from thelight source and reflected upon the inclining part can be directedtoward an arbitrary direction. Particularly, by reflecting light towardthe part where light is difficult to reach and is ready to darken, it ispossible to make even the brightness distribution on the surface lightsource device.

[0056] An eleventh surface light source device according to theinvention is in a surface light source device having a light source anda light conductor plate for spreading the light introduced from thelight source to nearly entire of a light emitting surface and emittingit from a light emitting surface, the surface light source devicecharacterized in that: the light source has a wavelength spectrum havinga plurality of peaks, the light conductor plate having a anti-reflectionfilm formed on the light emitting surface thereof, the anti-reflectionfilm has minimum values of reflective-index waveform dependency for aperpendicular incident light existing at a plurality of points, amaximum wavelength difference of the minimum values at the plurality ofpoints being greater than a maximum wavelength difference of a pluralityof peaks of the light source.

[0057] According to the eleventh surface light source device, even wherethe wavelength spectrum of the light source has a plurality of peaks asin a light-emitting diode, in case the maximum wavelength differencebetween a plurality of minimum values of reflective-index wavelengthdependency for a perpendicular incident light possessed by theanti-reflection film is greater than the maximum wavelength differencebetween a plurality of peaks of the light source, it is possible toeffectively suppress the shine due to the light of the light source.

[0058] A twelfth surface light source device according to the inventionis in a surface light source device having a light source and a lightconductor plate for spreading the light introduced from the light sourceto nearly entire of a light emitting surface and emitting it from alight emitting surface, the surface light source device characterized inthat: a plurality of concave-formed patterns are formed on the oppositeside of the light emitting surface of the light conductor plate,anti-reflection films different in reflection characteristic from eachother being formed on the light emitting surface of the light conductorplate and on an opposite surface thereto.

[0059] According to the twelfth surface light source device, becauseformed are anti-reflection films different in reflection characteristicfrom each other on the light emitting surface of the light conductorplate and the opposite surface, by selecting a proper film thicknessdepending upon a main or back surface of the light conductor film, it ispossible to effectively suppress the shine on the screen upon use on animage display unit. For example, the film thickness of ananti-reflection film is determined for the surface on the side formingthe concave-formed pattern in a manner preventing the reflection ofexternal light while the reflection due to the light-source light can besuppressed on the opposite side to the concave-formed pattern.Incidentally, this embodiment is effective for the case of using thesurface light source device as a front light.

[0060] A thirteenth surface light source device according to theinvention is in a surface light source device having a light source anda light conductor plate for spreading the light introduced from thelight source to nearly entire of a light emitting surface and emittingit from a light emitting surface, the surface light source devicecharacterized in that: the light conductor plate has a plurality ofconcave-formed patterns formed on the opposite side of the lightemitting surface, an anti-reflection film being formed on the oppositeside of the light reflection surface, the anti-reflection film having afilm thickness of the anti-reflection film at a boundary part between aplanar surface not in a concave-formed pattern and the concave-formedpattern different from a film thickness of the anti-reflection film inthe planar surface.

[0061] According to the thirteenth surface light source device, in theopposite surface to the light emitting surface of the light conductorplate, the anti-reflection film at a boundary between the concave-formedpattern and a planar surface is made different in film thickness fromthe planar surface. Accordingly, in the planar surface other than theconcave-formed pattern, the film thickness of the anti-reflection filmis determined in a manner preventing the reflection of external light.In the boundary at an edge of the concave-formed pattern, the filmthickness of the anti-reflection film is determined in a mannersuppressing the reflection due to the light-source light. In thismanner, by selecting a proper film thickness depending on a position,shine can be effectively prevented. Meanwhile, the shine due to externallight and the shine due to the light-source light can be suppressed moreeasily by controlling the film thickness rather than changing thematerial of the anti-reflection film. Incidentally, this embodiment iseffective particularly for the case of using the surface light sourcedevice as a front light.

[0062] Because the respective surface light source devices of theinvention are structured as in the above, there is no possibility tonarrow the directivity characteristic of the surface light source deviceto such an extent as causing flicker in the image. Meanwhile, becausethe directivity characteristic is restricted to certain narrowness,light loss is reduced and front brightness is improved.

[0063] A method for manufacturing a surface light source deviceaccording to the invention is a method for manufacturing a surface lightsource device according to claim 11, 15, 19 or 20 having a plurality ofconcave-formed patterns formed on the opposite side of the lightreflecting surface of the light conductor plate, the manufacturingmethod for a surface light source device comprises: a process ofinjection-forming a larger plate than a desired light conductor plate;and a process of cutting off undesired part of the plate.

[0064] According to the method for manufacturing a surface light sourcedevice according to the invention, instead of directly forming a lightconductor plate in a target form, a light conductor plate greater thanthat is first formed and thereafter it is cut to obtain an objectivelight conductor plate. Accordingly, a large-sized light conductor platecan be made in a form favorable in the resin fluidity during forming.Accordingly, it is possible to prevent the difficulty in achieving thepattern transferability for evenness over the entire surface due to theuneven resin flow during forming, or the readiness to cause warp in thelight conductor plate.

[0065] A liquid crystal display unit according to the inventioncomprises a liquid crystal display panel for generating an image and asurface light source device according to any one of claims 1 to 20 forlighting the liquid crystal display panel. According to the liquidcrystal display unit of the invention, the visibility of display on theliquid crystal display unit is improved for easy viewing.

[0066] A cellular phone according to the invention is in a cellularphone having a transceiver function, the cellular phone characterized bycomprising a display section including a liquid crystal display unitaccording to claim 22. According to the cellular phone of the invention,the visibility of display on the cellular phone is improved for easyviewing.

[0067] An information terminal unit according to the invention is in aninformation terminal unit having an information processing function, theinformation terminal unit characterized by comprising a display sectionincluding a liquid crystal display unit according to claim 22. Accordingto the information terminal unit of the invention, the visibility ofdisplay on the information terminal unit is improved for easy viewing.

[0068] Incidentally, the structural elements of this invention explainedabove can be combined to a possible extent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069]FIG. 1 is an exploded perspective view of a surface light sourcedevice having a conventional general structure;

[0070]FIG. 2 is a sectional view of the same surface light sourcedevice;

[0071]FIG. 3 is a view showing a directivity characteristic of a surfacelight source device of FIG. 1;

[0072]FIG. 4 is an exploded perspective view of a surface light sourcedevice having another conventional structure;

[0073]FIG. 5 is a view showing a directivity characteristic of the samesurface light source device;

[0074]FIG. 6 is a plan view showing a structure of a surface lightsource device in still another conventional structure;

[0075]FIG. 7 is a view showing a shape and operation of a diffusionpattern of the same surface light source device;

[0076]FIG. 8 is a view showing a directivity characteristic of thesurface light source device of FIG. 6;

[0077]FIG. 9 is a sectional view showing a surface light source devicein a conventional front-light type;

[0078]FIG. 10 is a view for explaining a desired directivitycharacteristic in the surface light source device;

[0079]FIG. 11 is a view representing one example of a directivitycharacteristic shown for comparison;

[0080]FIG. 12(a) is a characteristic view showing one example of apreferred directivity characteristic, FIG. 12(b) is a characteristicview showing one example of a more preferred directivity characteristic;

[0081]FIG. 13 is a figure representing an ideal directivitycharacteristic, the directivity characteristic in the case of using aprism sheet and a directivity characteristic in an x-axis direction andy-axis direction in the case of using a diffusion pattern;

[0082]FIG. 14 is a view stereoscopically representing a directivitycharacteristic of the light emitted from the surface light sourcedevice;

[0083]FIG. 15 is a schematic view showing a combination of areflective-type liquid crystal display panel and a front-light typesurface light source device (surface light source device);

[0084] (A) (B) (C) (D) in FIG. 16 is a figure showing a directivitycharacteristic of the surface light source device, and (a) (b) (c) (d)is a figure showing a corresponding reflection-light intensity angularcharacteristic of a reflective-type liquid crystal display panel;

[0085]FIG. 17(a) is a figure explaining a full-width at half maximum ina reflection light intensity—angle distribution of a reflective-typeliquid crystal display panel, and FIG. 17(b) is a figure explaining afull-width at half maximum in a directivity characteristic of a surfacelight source device;

[0086]FIG. 18 is an exploded perspective view showing a structure of asurface light source device according to a first preferred embodiment ofthe invention;

[0087]FIG. 19 is a view showing a behavior of the light in a plan formin a light emitting part used in the same surface light source device;

[0088]FIG. 20 is a figure showing a directivity characteristic of thelight emitted from the light emitting part of FIG. 19 using a regularreflection plate on a back surface;

[0089]FIG. 21 is a figure showing a directivity characteristic ofemission light in the case the regular reflection plate on the backsurface is replaced with a diffuse-reflection plate in the lightemitting part of FIG. 19;

[0090]FIG. 22 is a figure explaining how to determine a light intensity(energy) in a α direction in FIGS. 20 and 21;

[0091]FIG. 23(a) is a figure showing a directivity characteristic of thelight spread in a thickness direction (z-axis direction) of the lightconductor plate, FIG. 23(b) is a figure showing a directivitycharacteristic of the light spread in a widthwise direction (x-axisdirection) of the light conductor plate and FIG. 23(c) is a figureshowing a directivity characteristic of the light spread in a thicknessdirection and width wise direction (z-axis direction, x-axis direction)of the light conductor plate;

[0092]FIG. 24 is a figure showing a manner the direction of lightchanges when the light spread in the widthwise direction of the lightconductor plate is totally reflected upon a deflecting slant surface ofthe diffusion pattern;

[0093] FIGS. 25 (a) (b) is a figure representing another manner thedirection of light changes when the light spread in the widthwisedirection of the light conductor plate is totally reflected upon adeflecting slant surface of the diffusion pattern;

[0094]FIG. 26 is a figure showing a behavior of the light transmittedthrough the deflecting slant surface of the diffusion pattern andre-incident at the back surface on the light conductor plate;

[0095]FIG. 27(a) is a figure showing a direction of the light beforebeing incident on the diffusion pattern, FIG. 27(b) is a figure showinga direction of the light totally reflected upon a deflecting slantsurface of the diffusion pattern and the light of after reflection, andFIG. 27(c) is a figure showing a direction of the light transmittedthrough the deflecting slant surface of the diffusion pattern andre-incident at the back surface on the light conductor plate to beincident at the back surface and the light of after re-incidence;

[0096]FIG. 28 is a figure representing a light spatial frequency asviewed in a direction of light's traveling (y-axis direction) within thelight conductor plate;

[0097]FIG. 29 is a figure showing a directivity characteristic of thelight emitted at the light emitting surface of the surface light sourcedevice;

[0098]FIG. 30 is a figure explaining how to provide a diffusion patternin the case of introducing light obliquely from the light emitting partinto the light conductor plate;

[0099]FIG. 31 is a figure explaining how to examine a directivitycharacteristic of the light of within the light conductor plate;

[0100]FIG. 32 is a figure showing a behavior of the reflection lightupon a diffusion pattern sectionally in an arcuate form (comparativeexample);

[0101]FIG. 33 is a figure showing a behavior of the reflection lightupon a diffusion pattern sectionally in a saw-tooth form (comparativeexample);

[0102]FIG. 34(a) is a figure showing a behavior of the light totallyreflected upon a deflecting slant surface of a diffusion patternsectionally in a triangular form, and FIG. 34(b) shows a figure showinga behavior of the light transmitted through the diffusion pattern in thefront and reflected upon the diffusion pattern in the rear;

[0103]FIG. 35 is a figure showing a relationship between a lightemission angle from the surface light source device and a lightintensity when the angle of the deflecting slant angle is changed as 45,55, 65 degrees;

[0104]FIG. 36 is a figure showing a definition on an inclination angle γof a deflection slant surface in the diffusion pattern, an inclinationangle δ of a back surface and a light emission angle ε from a lightemitting surface;

[0105] FIGS. 37(a) (b) is a figure for explaining a relationship betweena light emission angle and a light intensity shown in FIG. 35, whereinthe same FIG. (a) shows a manner that the light incident nearlyhorizontally is reflected upon the deflecting slant surface while thesame FIG. (b) shows a manner that the light incident at the below isreflected upon the deflecting slant surface;

[0106]FIG. 38(a) shows a diffusion characteristic of a reflective-typeliquid crystal display panel, and FIG. 38(b) is a figure showing anemission-light intensity angular characteristic on the light conductorplate, and FIG. 38(c) is a figure showing an emission-light intensityangular characteristic from the reflective-type liquid crystal displaydevice;

[0107]FIG. 39 is a figure showing a behavior of the light transmittedthrough the deflecting slant surface to be re-incident at the backsurface where the inclination angle in a back surface of the diffusionpattern is small;

[0108]FIG. 40 is a figure showing a behavior of the light transmittedthrough the deflecting slant surface where the inclination angle in aback surface of the diffusion pattern is small;

[0109]FIG. 41(a) is a schematic view showing a traveling direction ofthe light to be introduced from a linear light source into the lightconductor plate, and FIG. 41(b) is a schematic view showing a travelingdirection of the light to be introduced from a plurality of spot lightsources arranged at an interval into the light conductor plate, and FIG.41(c) is a schematic view showing a traveling direction of the light tobe introduced from a plurality of spot light sources arranged collectedat one point into the light conductor plate;

[0110]FIG. 42 is a schematic side view showing a reflective-type liquidcrystal display unit using a surface light source device according to asecond preferred embodiment of the invention;

[0111]FIG. 43 is a magnifying sectional view showing a diffusion patternof the light conductor plate in the same surface light source device;

[0112]FIG. 44 is a schematic plan view of a surface light source deviceaccording to a third preferred embodiment of the invention;

[0113]FIG. 45 is a figure showing a directivity characteristic of thelight emitted from the same surface light source device;

[0114]FIG. 46 is a schematic plan view of a surface light source deviceaccording to a fourth preferred embodiment of the invention;

[0115]FIG. 47 is a magnifying plan view of a diffusion pattern providedon the light conductor plate of the same surface light source device;

[0116]FIG. 48 is a modification to the same diffusion pattern;

[0117]FIG. 49 is a figure showing a winding diffusion pattern and thelight incident thereon;

[0118]FIG. 50 is a figure showing a directivity characteristic of thelight L4 reflected at a point-e in FIG. 49;

[0119]FIG. 51(a) is a figure viewing in a z-axis direction a directionof the light L4, L5, L6 reflected at a point-e point-f, point-g in FIG.49, and FIG. 51(b) is a figure showing the light of C1, C2 of the sameFIG. (a) to be reflected upon the deflecting slant surface;

[0120]FIG. 52 is a figure showing a light emitting region of the lightshown in FIG. 49;

[0121]FIG. 53 is a perspective view of the surface light source deviceaccording to a fifth preferred embodiment of the invention;

[0122]FIG. 54 is a side view showing a behavior of the light in the samesurface light source device;

[0123]FIG. 55 is a figure showing a relationship between the angledefined by a direction parallel with the light emitting surface (y-axisdirection) and an emission light and an emission-light intensity whenusing a regular reflection plate on a back surface of the lightconductor plate;

[0124]FIG. 56 is a figure showing a relationship between the angledefined by a direction parallel with the light emitting surface (y-axisdirection) and an emission light and an emission-light intensity whenusing a diffuse-reflection plate on a back surface of the lightconductor plate;

[0125]FIG. 57 is a schematic side view of a surface light source deviceusing a light conductor plate formed with different structured diffusionpatterns;

[0126]FIG. 58 is a schematic side view of a surface light source deviceusing a light conductor plate formed with further different structureddiffusion patterns;

[0127]FIG. 59 is a schematic view of a comparative example using aplurality of spot light sources;

[0128]FIG. 60 is a schematic perspective view partly broken away showinga comparative example using a plurality of spot light sources andcylindrical lenses;

[0129]FIG. 61 is a schematic plan view showing a surface light sourcedevice using a plurality of spot light sources and concave mirrors toemit a light having a narrow directivity;

[0130]FIG. 62 is a plan view showing a surface light source deviceaccording to a sixth preferred embodiment of the invention;

[0131]FIG. 63 is a schematic side view showing a liquid crystal displayunit using the surface light source device of FIG. 62 as a backlight;

[0132]FIG. 64 is a schematic side view showing a liquid crystal displayunit using the surface light source device of FIG. 62 as a front light;

[0133]FIG. 65(a) is a plan view showing a winding diffusion pattern, andFIG. 65(b) is a J-J line sectional view of the same FIG. (a);

[0134]FIG. 66 is a is a view showing the spread of the light reflectedupon the deflecting slant surface of the same diffusion pattern;

[0135]FIG. 67 is a view showing the light transmitted through the samediffusion pattern;

[0136]FIG. 68(a) is a plan view of a light conductor plate provided withthe same diffusion pattern, and FIG. 68(b) is a part-A magnifying viewof the same FIG. (a), FIG. 68(c) is a part-B magnifying view of the sameFIG. (a), and FIG. 68(d) is a part-C magnifying view of the same FIG.(a);

[0137]FIG. 69 is a figure showing a relationship between a distance fromthe light emitting part (light source) and a pattern density ofdiffusion patterns in the same light conductor plate;

[0138]FIG. 70 is a figure showing a relationship between a distance fromthe light emitting part and a pattern length of diffusion patterns inthe same light conductor plate;

[0139]FIG. 71 is a figure showing a relationship between a distance fromthe light emitting part and a pattern count density (pattern count/area)of diffusion patterns in the same light conductor plate;

[0140]FIG. 72 is a schematic view showing a structure and an operationthereof for sending much more light to a corner in the light emittingsurface in the same surface light source device;

[0141]FIG. 73 is a schematic view showing a light conductor plate fittedwith a fixing frame;

[0142]FIG. 74 is a magnifying sectional view partly broken away showingan anti-reflection film formed on a side of a patterned surface of thesame light conductor plate;

[0143]FIG. 75 is a figure showing a relationship between a wavelength ofa light-emitting diode and an emission-light intensity;

[0144]FIG. 76 is a figure showing a relationship between an incidentlight wavelength and reflective index in the anti-reflection film;

[0145]FIG. 77 is a schematic view explaining on how to form ananti-reflection film having a great thickness on an edge of thediffusion pattern;

[0146]FIG. 78 is a view showing the light as shine due to reflectionupon the patterned surface of the light conductor plate, the lightemitting surface and the like and an anti-reflection film provided onthe patterned surface of the light conductor plate and light emittingsurface;

[0147]FIG. 79 is a figure showing an emission-light intensity wavelengthcharacteristic of the light emitted from a white light-emitting diode;

[0148]FIG. 80 is a sectional view showing a structure of a lightemitting part attached on the light conductor plate;

[0149]FIG. 81 is a side view showing a liquid crystal display unitmounted on a circuit board;

[0150]FIG. 82 is a figure showing a resin flow upon forming arectangular light conductor plate within a rectangular cavity of a molddie;

[0151]FIG. 83 is a view showing a manner of forming with a mold diehaving a cavity greater than a target light conductor plate and smoothin resin flow;

[0152]FIG. 84 is a front view of a cellular phone;

[0153]FIG. 85 is a front view of a PDS;

[0154]FIG. 86(A) (a) is a figure showing an emission-light intensitydistribution of the light emitted from the light conductor plate, FIG.86(B) (b) is a figure showing an intensity distribution of the lightreflected at a lower surface of the light conductor plate and emittedfrom the light emitting surface, FIG. 86(C) (c) is a figure showing adiffusion characteristic of a liquid crystal display panel, FIG. 86(D)(d) is a figure showing an emission-light intensity distribution of fromthe liquid crystal display panel, and FIG. 86(E) (e) is a figure showingan S/N ratio during lighting of the surface light source;

[0155]FIG. 87 is a plan view showing a diffusion pattern used on asurface light source unit according to a seventh preferred embodiment ofthe invention; and

[0156]FIG. 88(a) is a schematic view of a surface light source unitaccording to an eighth preferred embodiment of the invention, and FIG.88(b) is a view for explanation by comparison.

BEST MODE FOR CARRYING OUT THE INVENTION

[0157] With reference to the drawings, preferred embodiments of thepresent invention will be explained in detail in the below.

[0158] With a portable apparatus such as a cellular phone, it is oftenthe case for one person to view the display (liquid crystal displaydevice) without requiring a wide view angle. According to an experiment,in the case of viewing a screen of a portable apparatus while walking,unless light is emitted only within 10 degrees as measured in adirection perpendicular to the screen, there has been flicker wheneverthe screen has been swung in viewing direction. However, it has beenconfirmed that in case a direction of light emission is approximately 20degrees, sufficiently 30 degrees or greater, with respect to a directionperpendicular to the screen, it is easy to view it.

[0159] From this result, it can be seen that the light emitted to theoutward greater than 20 to 30 degrees as measured in a directionperpendicular to the screen results in a loss lowering the visibility onthe liquid crystal display device. In other words, in order to makepreferable the light utilization efficiency of a surface light sourcedevice and improve the visibility of a liquid crystal display device, itis considered satisfactory to provide the light emitted from the surfacelight-source device with a directivity broader than approximately 10degrees but narrower than approximately 20-30 degrees.

[0160] However, the directivity of the light emitted from a lightconductor plate can be easily broadened by using a diffusion plate.Conversely, there is difficulty in narrowing it. The use of a prismsheet allows aligning the direction of light. However, the light oncespread in a light-emitting direction is difficult to align to a narrowrange even by using a prism sheet. Also, it is preferred not to use aprism sheet in order to prevent the increase in the thickness of asurface light-source device.

[0161] Accordingly, in order to fabricate a surface light source deviceexcellent in efficiency and visibility, the more preferable the higheris the ratio, to the light emitted from the light conductor plate, ofthe light emitted within 20 to 30 degrees as measured with respect to anormal line given on a light emission surface, wherein a prism sheet isnot used. It is preferred to emit light to within the area at a ratio ofat least a half or more, preferably two-thirds or more.

[0162] Incidentally, the direction of the light emitted from the surfacelight source device is a direction of a normal line given on alight-emitting surface of the surface light source device 41 (lightconductor plate), as shown in FIG. 10 (hereinafter, this directionrefers to a z-axis direction, a direction parallel with a pair of sidesof the surface light source device refers to an x-axis direction, and adirection parallel with the remaining pair of sides refers to a y-axisdirection). For example, a direction of within θ=30 degrees, whenmentioned, refers to every direction of within θ=30 degrees with respectto the z-axis, which refers to a direction of the light emitted directedto a hatched area of FIG. 10. Taking one example, in the case of asurface light source device for emitting light in a manner turning intonearly a Lambertian light at within a z-x plane as shown in FIG. 11,there is less light contained within 30 degrees as viewed in a directionperpendicular to the z-x plane. However, nearly all the light iscontained within 30 degrees as viewed in a direction perpendicular to ay-z plane. In such a case, nearly all the light is not emitted in thedirection of within 30 degrees, in the sense as used in the presentspecification. Namely, when mentioning is made in this specificationthat light is emitted in a direction of within 30 degrees for example,light emission must be made in a direction of within 30 degrees asviewed not only in one direction but also in every direction.

[0163]FIG. 12(a) represents a directivity characteristic of a light themajor part of which is emitted to within θ from the surface light sourcedevice 41. Considering an ideal directivity characteristic of the lightemitted from the surface light source device 41, it is preferred thatbrightness is even in an inside range of θ=20-30 degrees (40-60 degreesin the overall width) while no brightness is given in the innerdirection than that as shown in FIG. 12(b). By realizing such adirectivity characteristic, there is no occurrence of image brightnesschange and flicker even if the viewing direction is changed (even ifthere is swing in screen angle). Meanwhile, despite there is differencein viewing angle at between a center and an end of the screen,brightness is provided constant. This results in easiness in viewing thescreen.

[0164] Such an ideal directivity characteristic, if represented with anemission angle taken on a horizontal axis and brightness on aperpendicular axis, is given as a rectangular-formed characteristic asshown by a two-dot chain line in FIG. 13. It is difficult to correctlyrealize such a directivity characteristic. However, despite notobtaining such an ideal directivity characteristic, if it is assumedthat emission light is emitted in a direction nearly perpendicular tothe light emitting surface (z-axis direction), a half or more of thetotal emission light is contained within an area having a half of themaximum brightness in an emission-light brightness angular distribution,and as shown in FIG. 14, the area has a width (entire-width angle) ofΔθx and Δθy respectively in an x-direction and a y-direction, then amore preferred directivity characteristic is obtained by providing atleast

30°≦Δθx≦70°

30°≦Δθy≦70°.

[0165] Furthermore, a desirable directivity characteristic is obtainedprovided that

40°≦Δθx≦60°

40°≦Δθy≦60°.

[0166] Next, consideration is made on a case of a surface light sourcedevice 41 to be used as a front light. For a surface light source device41 of a front light type, there is a need to consider a relationshipwith a reflection light angle characteristic of a reflection type liquidcrystal display panel 42. Herein, the reflection light anglecharacteristic of a reflection type liquid crystal display panel 42refers to an angle dependency of reflection light intensity wherecollimated light is incident on the reflection type liquid crystaldisplay panel 42, as shown in FIG. 15. FIGS. 16(A) (B) (C) (D)represents directivity characteristic of a front-light type surfacelight source device 41, wherein the directivity characteristic isgradually broadened from (A) toward (D). Meanwhile, FIGS. 16(a) (b) (c)(d) represents a reflection-light angle characteristic of a reflectiontype liquid crystal display panel 42, wherein (a) (b) (c) (d)respectively corresponds to the directivity characteristic A) (B) (C)(D).

[0167] As shown in FIG. 16, as the directivity characteristic of thesurface light source device broadens, the reflection light intensityangle characteristic of the liquid crystal display panel 42 is graduallymoderated. In the case that the directivity characteristic of thesurface light source device 41 becomes broader than the reflection lightintensity angle characteristic of the liquid crystal display panel 42 asin FIG. 16 (D) (d), there is decrease in the perpendicular componentintensity of the light reflected upon the liquid crystal display panel42 as compared to the case having a directivity characteristic of thesurface light source device 41 narrower than a reflection lightintensity angle characteristic of the liquid crystal display panel 42 asin FIGS. 16(A) (a); (B) (b); (C) (c).

[0168] Mentioning on the case shown in FIG. 16, of the light emittedfrom the surface light source device 41, the light reflected at an angleoutside 30 degrees or its around as measured with respect to an axisperpendicular to the liquid crystal display panel 42 substantiallyresults in loss.

[0169] Accordingly, in the case of the front-light type surface lightsource device 41, it is preferred to narrow the directivitycharacteristic to emit a half or more, desirably two-thirds or more, ofthe emission light of the surface light source device 41 to within anangular range of a full-width at half maximum of the reflection lightintensity angular distribution of the reflection-type liquid crystaldisplay panel 42. It is noted that the full-width at half maximum of thereflection light intensity angular distribution of the reflection-typeliquid crystal display panel 42 refers to an angle of between the twopoints having a half value of the maximum value as shown in FIG. 17(a).However, the directivity characteristic of the surface light sourcedevice 41 has, in some cases, a sharp peak at a center. Accordingly, asshown in FIG. 17(b), the angle of between the two points having a halfof the intensity in a position off a center peak position, e.g. aposition distant by approximately 5 degrees from a peak, is referred toas a full-width at half maximum.

[0170] In the below, explanations will be made on various embodiments ofsurface light source devices having a characteristic approximate to anideal directivity characteristic as noted above.

[0171] (First Preferred Embodiment)

[0172] First, FIG. 18 is an exploded perspective view showing astructure of a backlight-type surface light source device 43 accordingto a first preferred embodiment of the present invention. This surfacelight source device 43 is structured with a transparent light conductorplate 44 and a light emitting part 45 arranged oppositely to a lightincident surface 44 a of the light conductor plate 44. The lightconductor plate 44 is formed in a rectangular plate form of atransparent resin having a high refractive index (e.g. polycarbonateresin, methacrylic resin or the like). This has a lower surface having aplurality of strips of diffusion patterns 46 formed parallel one withanother to extend over nearly entire widthwise length. The diffusionpattern 46 has a section nearly in a rectangular triangular formstructured with a deflecting slant surface 46 a at a light-source sideand a nearly perpendicular surface in a rear surface (light re-incidentsurface) 44 b. The diffusion patterns 46 are formed by cutting the lowersurface of the light conductor plate 44. These are formed with a spacingfrom one another. The spacing between the diffusion patterns 46decreases with increase in distance from the light incident surface 44a.

[0173] The light emitting part 45 has a wedge-like light conductor 47formed of a transparent resin having a high refractive index(hereinafter, referred to as a wedge-like light conductor), a smalllight source (hereinafter, referred to as a spot light source) 48arranged oppositely to a side end surface of the wedge-like lightconductor 47, a regular reflection plate 49 arranged on a rear surfaceof the wedge-like light conductor 47, and a prism sheet 50 arranged infront of the wedge-like light conductor 47. Herein, the spot lightsource 48 is sealed with one or a plurality of light-emitting diodes ina transparent resin. The transparent resin is covered, excepting itsfront surface, with a white resin. The light emitted from thelight-emitting diode is efficiently emitted toward the front directly orafter reflection upon an inner surface of the white resin (see FIG. 80).

[0174] The light emitted from the spot light source 48 (Lambertianlight) is incident on the wedge-like light conductor 47 at a side endsurface of the wedge-like light conductor 47. The light entered in thewedge-like light conductor 47 repeatedly reflects upon a front surface(light emitting surface) 47 a and a rear surface of the wedge-like lightconductor 47 to travel within the wedge-like light conductor 47 as shownin FIG. 19. Each time of reflection on the rear surface of thewedge-like light conductor 47, decreased is the incident angle on thefront surface 47 a. At a point where the incident angle on the frontsurface 47 a of the wedge-like light conductor 47 is smaller than acritical angle of total reflection, the light is emitted at the frontsurface 47 a of the wedge-like light conductor 47 to the outside.Meanwhile, as shown with a broken line in FIG. 19, the light emittedoutside at the rear surface of the wedge-like light conductor 47 isreflected upon a regular reflection plate 49 to be returned again intothe wedge-like light conductor 47, then being emitted at the frontsurface 47 a of the wedge-like light conductor 47. In this manner, thelight emitted at the front surface 47 a of the wedge-like lightconductor 47 is aligned into a direction nearly parallel with the frontsurface 47 a of the wedge-like light conductor 47 (generally in anegative direction on the x-axis).

[0175] The prism sheet 50, arranged on the front surface 47 a of thewedge-like light conductor 47, is formed of also a transparent resinhaving a high refractive index (e.g. a transparent resin having arefractive index 1.59). The prism sheet 50 has a plurality of prisms 50a arranged on a front surface thereof. Each prism 50 a is sectionally ina triangular form having an apex angle of 40 degrees to extend in aperpendicular direction (in a thickness direction of the light conductor44). Consequently, the light emitted at the front surface 47 a of thewedge-like light conductor 47 in the above manner transmits the prism 50a and refracted whereby it is deflected to a direction nearlyperpendicular to the prism sheet 50 and then incident nearlyperpendicularly on the light conductor plate 44 at the light incidentsurface 44 a. Consequently, according to the light-emitting part 45, thelight emitted from the spot light source 48 can be emitted with spreadover nearly entire length of the prism sheet 50. Thus, the spot lightsource 48 can be converted into so-called a linear light source.

[0176] Incidentally, there is a case that the light transmitted throughthe prism sheet 50 in a part turns into stray light due to the formingerror of apex roundness in a prism section of the prism sheet 50 orFresnel reflection. Consequently, in order to deflect at least a half ormore of the light emitted from the spot light source 48 by the prismsheet 50 to be incident at a desired angle (in a direction perpendicularto the light incident surface 44 a, in this embodiment) on the lightconductor plate 44, it is preferred that the light emitted, at the frontsurface 47 a of the wedge-like light conductor 47, in parallel with thefront surface 47 a has a ratio of two-thirds or greater to all theemission light of from the spot light source 48.

[0177] Considering, for comparison, a case using a diffuse-reflectionplate on the rear surface of the wedge-like light conductor 47 in placeof the regular reflection plate 49, the light emitted, at the frontsurface 47 a of the wedge-like light conductor 47, along the frontsurface 47 a is a half or less of the total amount of the light emittedfrom the spot light source 48. This is because of the reason that, asthe light shown by the broken line in FIG. 19, the light leaked at therear surface of the wedge-like light conductor 47 strikes thediffuse-reflection plate where it is reflected nearly in Lambertiandistribution, so that less light is emitted along the front surface 47 aof the wedge-like light conductor 47 (nearly in a negative direction onx-axis).

[0178] Although it was already mentioned that the light-emitting part 45structured as in this embodiment can convert the spot light source intoa linear light source, furthermore the light emitted from the linearlight source can be aligned nearly even in direction. FIG. 20 shows, ina form arranged with a regular reflection plate giving equal incidentand emitting angles without diffusive action on the rear surface of thewedge-like light conductor 47, shown is a result of a measurement on arelationship between an angle α of the emission light from thewedge-like light conductor 47 defined relative to the front surface 47 athereof (negative direction on x-axis) (see FIG. FIG. 19) and anintensity of the light in that direction. FIG. 21 shows, in a case ofreplacing the regular reflection plate on the rear surface of thewedge-like light conductor 47 with a diffuse-reflection plate, shown isa result of a measurement on a relationship between an angle a of theemission light from the wedge-like light conductor 47 defined relativeto the front surface 47 a thereof (negative direction on x-axis) (seeFIG. FIG. 19) and an intensity of the light in that direction. Thismeasurement uses a wedge-like light conductor 47 having a length 30 mm,a thickness 1 mm, a width of a side surface to which a spot light source48 opposes 2 mm and a refractive index 1.53, and a regular reflectionplate or diffuse-reflection plate having a length of approximately 30mm. Meanwhile, measurement was made in a state the prism sheet 50 wasremoved.

[0179] Incidentally, in the graphs shown in FIGS. 20 and 21, the lightintensity (energy) in an α direction does not signify an angulardistribution of intensity of the light emitted in the α direction on aplane perpendicular to the front surface 47 a of the wedge-like lightconductor 47 (x-y plane in FIG. 22). Instead, it is a representation ofan intensity of the light contained in a unit angle (dα=1) in the αdirection where the emission light at the front surface 47 a is allprojected onto the relevant plane.

[0180] As can be seen from FIG. 20, in the case of using a regularreflection plate, light intensity reaches the maximum at a direction ofnearly, slightly smaller than 30 degrees. In a range of 0 to 40 degrees,there is light concentration of 98% of the total light amount. Even ifthis is deflected by the prism sheet 50 and incident on the lightconductor plate 44 whereupon, should nearly 10% of loss occur due tomanufacture error of the prism sheet 5, 80% or more of the light can bealigned to within a range of ±13 degrees as viewed from the above(z-axis direction). Contrary to this, as shown in FIG. 21, in the caseof using a highly-diffusive reflection plate as in usual use, only 52%of light concentrates within the range of 0 to 40 degrees. Moreover, incase loss is added due to the prism sheet 50, it is impossible to narrowthe directivity at within the light conductor plate 44.

[0181] Consequently, according to such a light-emitting part 45, lightemission is possible over a long range as in a linear light source bythe use of the spot light source 48, such as light-emitting diodes, andthe wedge-like light conductor 47. Moreover, the Lambertian lightemitted from the spot light source can be aligned nearly evenly andemitted as a light narrow in directivity.

[0182] In this manner, the light incident at the light incident surface44 a on the light conductor plate 44 travels from a proximate side tothe light-emitting part 45 toward a distal side within the lightconductor plate 44 while repeating total reflection at between the uppersurface (light emitting surface 44 b) and the lower surface of the lightconductor plate 44. Then, when this is incident on a triangulardiffusion pattern 46 provided in a bottom surface of the light conductorplate 44, a part thereof is reflected upon the diffusion pattern 46 andemitted at the light emitting surface 44 b. Because the triangulardiffusion pattern 46 is made long in the x-axis direction, the lighteven if reflected by the diffusion pattern 46 does not change in itsdirectivity in the x-axis direction. Accordingly, the light narrow indirectivity in the x-axis direction aligned by the light-emitting part45, after reflected upon the diffusion pattern 46 and emitted in thez-axis direction, is kept narrow in its directivity in the x-axisdirection. On the other hand, the light propagating in the lightconductor plate 44 has a spread in the z-axis direction. However, thespread turns into a spread in they-axis direction upon reflection in thez-axis direction by the diffusion pattern 46. However, the spread in they-axis direction can be narrowed by restricting the angle of the lightbeing reflected by the diffusion pattern. Thus, the light after emittedat the light emitting surface 44 b can be made narrower in thedirectivity in the y-axis direction than a directivity in the z-axisdirection of within the light conductor plate 44. In a typical example,the directivity of the light exited at the light emitting surface 44 bof the light conductor plate 44 as viewed in the x-axis direction, inthe overall width, is within a range of approximately 55 degrees aboutthe z-axis direction, while the directivity thereof as viewed in they-axis direction, in the overall width, is within a range ofapproximately 25 degrees about the z-axis direction.

[0183] Consequently, according to the surface light source device 43, itis possible to emit light in a direction perpendicular to the surfacelight source device 43 without the use of a prism sheet or the like, andto narrow the directivity thereof. It is possible to realize adirectivity characteristic approximate to the ideal directivitycharacteristic. Because of no use of a prism sheet, the surface lightsource device 43 can be cost-reduced and the surface light source device43 can be reduced in thickness.

[0184] Contrary to this, in a method for enhancing a directivity oflight by laminating two prism sheets having patterns made orthogonal toeach other, the directivity characteristic of light is given as apattern as shown by a broken line in FIG. 13. Even where the lightbefore entering the prism sheet has a directivity of ±30 degrees, thelight after passing the two-laminated prism sheets could not haveemitted a half or more to within a range of ±20 degrees.

[0185] Meanwhile, in this surface light source device 43, the diffusionpatterns 46 have an increased interval in an area close to the lightemitting part 45 while the interval of the diffusion patterns 46 isgradually decreased as distant from the light emitting part 45. Due tothis, brightness is made even on the entire of the light emittingsurface 44 b of the light conductor plate 44.

[0186] Next, explanation will be made in detail on the operation of thediffusion pattern 46 sectionally in a triangular form. Now, thedirectivity of the light before incidence on the diffusion pattern 46 isconsidered on a case that is narrow only in the x-axis direction as inFIG. 23(a), a case that is narrow only in the z-axis direction as inFIG. 23(b) and a case that is narrow only in the x-axis and z-axisdirections as in FIG. 23(c). Of these, such a case as in FIG. 23(c) isfree from a narrow directivity in any direction unlike FIGS. 22(a) and(b) and hence excluded.

[0187] Next, considered is a case that the light having a directivitynarrow only in the z-axis direction is incident on the diffusion pattern46 as shown in FIG. 23(b). In this case, as shown in FIG. 24, in caseall the light incident on the diffusion pattern 46 is totally reflectedupon the deflecting slant surface 46 a of the diffusion pattern 46,there is no change in directivity of the light reflected upon thediffusion pattern 46. In particular, the directivity in the x-axisdirection is not narrowed. Consequently, as shown in FIGS. 25(a) (b), incase the deflecting slant surface 46 a of the diffusion pattern 46 isincreased in its inclination angle to reflect a part of the light uponthe diffusion pattern 46 to transmit the part of the light, the lighttotally reflected upon the deflecting slant surface 46 a of thediffusion pattern 46 is emitted in a direction largely inclined relativeto the z-axis. This also transmits through the deflecting slant surface46 a of the diffusion pattern 46 as shown in FIG. 26. The lightre-incident on the rear surface 46 b is changed in its angle uponre-incidence. Thus, the directivity in the z-axis direction iscollapsed. Accordingly, as shown in FIG. 23(b), for the light having adirectivity narrow only in the z-axis direction, there is extremedifficulty in narrowing the directivity also in the x-axis direction.

[0188] Contrary to this, as shown in FIG. 23(a), for the light having adirectivity narrow only in the x-axis direction, when it is incident onthe deflecting slant surface 46 a of the diffusion pattern 46sectionally in a triangular form long in the x-axis direction, even ifit before incidence has a relatively great spread in the z-axisdirection as in FIG. 27(a), if a part of the light is totally reflectedon the deflecting slant surface 46 a of the diffusion pattern 46 as inFIG. 27(b) while a part of the light is caused to transmit through thedeflecting slant surface 46 a as in FIG. 27(c) and re-incident on therear surface 46 b, then the light reflected upon the diffusion pattern46 can be limited in region to one part. Accordingly, it is possible tonarrow the directivity in the y-axis direction of the light totallyreflected on the diffusion pattern 46 and emitted at the light emittingsurface 44 b. Moreover, by setting the inclination angle of thedeflecting slant surface 46 a of the diffusion pattern 46 to a propervalue, the light reflected upon the diffusion pattern 46 can be easilyemitted in a direction nearly perpendicular to the light emittingsurface 44 b (in the z-axis direction). On the other hand, because thediffusion pattern 46 extends evenly in the x-axis direction, there is nospread of directivity in the x-axis direction even where totalreflection is done upon the diffusion pattern 46. Meanwhile, as shown inFIG. 27(c), the light transmitted through the deflecting slant surface46 a of the diffusion pattern 46 and re-incident at the rear surface 46b changes in traveling angle on the y-z plane. However, because thedirectivity in the z-direction is not narrow in its nature, there is nopossibility of directivity broadening in the z-axis direction.Incidentally, the center light L2 in FIG. 27(a) represents a light to beincident at an angle slightly greater or slightly smaller than acritical angle of total reflection on the deflecting slant angle 46 a ofthe diffusion pattern 46.

[0189] Although the explanation using FIGS. 23(a) and 27 explained onthe case not having light spread in the x-axis direction at all,actually the light emitted from the light emitting part 45 has a spreadmore or less even in the x-axis direction. For example, when consideringa space frequency as viewing the light propagating in the lightconductor plate 44 in a y-axis direction, the light is consideredconcentrated in a hatched region in FIG. 28. Herein, the light on acenter line-j parallel with the z-axis direction is a light traveling onthe y-z plane, while the light on a line-i parallel therewith representsa light inclined toward the x-axis direction relative to that. In thecase that the diffusion pattern 46 extends perfectly parallel with thex-axis and furthermore the deflecting slant surface 46 a of thediffusion pattern 46 and the rear surface 46 b extend parallel with eachother in the plan view, there is no change of the light space frequencyin the x-axis direction due to the reflection upon or transmissionthrough the diffusion pattern 46. For this reason, on the x-y plane, thedirection of light s traveling in the light conductor plate 44 does notchange as long as no light is emitted. There is nothing more thantransfer of the light on the line-i to the line-i and of the light onthe line-j to the line-j.

[0190] Accordingly, in case the directivity in the x-axis direction isnarrowed in the light emitting part 45 and thereafter the same light isreflected upon the diffusion pattern 46 to thereby narrow thedirectivity thereof in the y-axis direction, the light emitted in thez-axis direction from the surface light source device 43 is narrowed inits directivity in both the x-axis and y-axis directions. In conclusion,this makes it possible to emit a light having a directivity narrow inevery direction, as shown in FIG. 29.

[0191] In the meanwhile, in order to reduce the directivity in thex-axis direction of the light to be emitted from the light conductorplate 44 down to ±20 degrees or smaller, there is a need to provide adirectivity in the x-axis direction of ±13 degrees or smaller at withinthe light conductor plate 44. The numeral of ±13 degrees or smaller isdue to a calculation by taking a refractive index of the light conductorplate 44 of 1.53. However, the transparent resin to be used for thelight conductor plate 44 has a refractive index of approximately1.4-1.65. Within this range, there is no significant change in thedirectivity angle in the x-axis direction required in the lightconductor plate 44. Also, even where the refractive index changesfurthermore, practically there is no significant change in the value of13 degrees. Accordingly, this value may be targeted in designing a lightemitting part 45.

[0192] In the case that a center of light in a traveling direction(center of a spread of ±13 degrees or smaller) is in parallel with they-axis direction, the diffusion pattern 46 may be made parallel with thex-axis direction. However, as shown in FIG. 30, in the case that acenter of light in a traveling direction is inclined relative tothey-axis direction, in order to correct it the diffusion pattern 46 inits extending direction may also be placed inclined relative to thex-axis direction to make the direction of light s traveling and theextending direction of the diffusion pattern 46 perpendicular to eachother in the plan view (on the x-y plane).

[0193] It is noted that, in a surface light source device of such ascheme, because the light traveling in the light conductor plate 44 hasan extremely narrow directivity, in the case that the light center inthe traveling direction, is inclined from the y-axis direction, thereoccurs darkening at a corner D in the light conductor plate 44 as shownin FIG. 30. Consequently, on the light conductor plate having such arectangular light-emission area, it is preferred that the light centerin a traveling direction is in a direction perpendicular to the lightincident surface 44 a or at least within ±13 degrees with respect to thedirection perpendicular to the light incident surface 44 a. Meanwhile,as for the diffusion pattern 46, in case the light center in a travelingdirection and the diffusion pattern 46 are within a range of ±13 degreesinstead of perfectly perpendicular, there is no problem because theperpendicular direction to the light emitting surface 44 b of thesurface light source device 41 is included within an emission-lightangular range of ±20 degrees.

[0194] Incidentally, in the case of examining a directivitycharacteristic of the light of in the light conductor plate 44, thelight conductor plate 44 is cut on the plane parallel with the z-axisand nearly perpendicular to the direction of light's traveling as shownin FIG. 31. By measuring an angular intensity distribution of the lightemitted at the cut surface C-C, it is possible to calculate an angularintensity distribution of within the light conductor plate 44, from theSnell's law.

[0195] Next, explanation will be made on a shape, a designing method andthe like of individual diffusion patterns. Where the diffusion pattern46 is nearly perpendicularly arranged relative to a traveling directionof the light in the light conductor plate 44, a sectionally triangularform of pattern is suited for the diffusion pattern 46 as noted before.In the case of a diffusion pattern 51 formed with a curve surface asshown in FIG. 32, the deflecting direction of light is differentdepending on a point of light reflection, thus broadening the angularrange of emission light. Accordingly, not preferred is the pattern thusconfigured with a curve surface in a section perpendicular to alengthwise direction. Meanwhile, in the case of a diffusion pattern 52in a saw-tooth form as shown in FIG. 33, the light transmitted throughthe diffusion pattern 52 is not emitted in a direction perpendicular tothe light emitting surface 44 b but all emitted in useless directions.Consequently, such a saw-tooth patterned diffusion pattern 52 is alsonot preferred.

[0196] Contrary to this, in the case of a diffusion pattern 46sectionally in a rectangular triangular form having a rear surface 46 bperpendicular to a lower surface of the light conductor plate 44, asshown in FIG. 34(a) the light totally reflected upon the deflectingslant surface 46 a, even when all the light is reflected, is reflectedwhile keeping directivity. In the case that a part transmits through thediffusion pattern 46, there is narrowing in the directivity. Meanwhile,as shown in FIG. 34(b), the light transmitted through the diffusionpattern 46, after being re-incident at the rear surface 46 b withoutimpairing the directivity, can be totally reflected upon anotherdiffusion pattern 46. Incidentally, although the rear surface 46 b ispreferably perpendicular to the lower surface of the light conductorplate 44, a somewhat inclination is provided in view of difficulty indie removal during molding.

[0197] It is noted that, for such a diffusion pattern 46 sectionally ina rectangular triangular form, where the light in the light conductorplate is not aligned in direction as viewed at the upper surface (spreadis greater in the x-axis direction), there is a reduced ratio of thelight perpendicularly striking the diffusion pattern 46 with increase ofthe light obliquely striking it. The obliquely striking light as viewedat the upper surf ace has an increased incident angle on the diffusionpattern 46 as compared to the perpendicularly striking light, to have anincreased ratio of reflection. Namely, there is decrease in the effectof re-incidence on the diffusion pattern 46 (the effect of narrowingdirectivity without decreasing the utilization efficiency of light).Accordingly, for the diffusion pattern 46 sectionally having arectangular triangular form, in order to enhance the effect of thediffusion pattern 46, there is a need that the light is aligned in itstraveling direction within the light conductor plate 44 and thediffusion pattern 46 is arranged rectangular to the traveling direction.Otherwise, for the case with the present embodiment, it is premised thatthe directivity in the x-axis direction is made narrow by the lightemitting part 45.

[0198] Consideration will be made on an inclination angle γ of thedeflecting slant surface 46 a of the diffusion pattern 46. FIG. 35 is anangular distribution of emission light intensity when taking theinclination angles γ of 45, 55 and 65 degrees, wherein the horizontalaxis represents an emission angle ε of the emission light shown in FIG.36 while the perpendicular axis represents an emission light intensity.In FIG. 35, the reason of the increase of luminosity on a minus side ofan emission angle ε is because the light having a greater emission anglehas a less light striking the deflecting slant surface 46, as shown inFIGS. 37(a) (b). Otherwise, when viewed on the y-z plane, the light inthe light conductor plate 44 nearly parallel with the deflecting slantsurface 46 a has an emission light intensity of zero (such light doesnot exist in many cases), wherein the intensity of emission lightincreases with increase in the distance from such an angle, i.e. withdecrease in the emission angle ε (with increase on the minus side).Seeing FIG. 35, in the case of γ=55 degrees, the emission angle ε is onthe minus side wherein the angular range of emission light is somewhatless but the intensity correspondingly great so that balance is providedbetween the minus and plus side of emission angle ε.

[0199]FIG. 38(a) shows a diffusion characteristic of a reflective-typeliquid crystal display panel having a diffusion action of approximately25 degrees. FIG. 38(b) shows an emission light angular characteristic ofa surface light source device having a diffusion pattern 46 of aninclination angle of γ=55 degrees. FIG. 38(c) represents an emissionlight angular characteristic of from a reflective-type liquid crystaldisplay panel where the light of a surface light source device havingsuch a characteristic as of FIG. 38(b) is incident on thereflective-type liquid crystal display panel having such acharacteristic as of FIG. 38(a). As shown herein, in case the surfacelight source device having a diffusion pattern 46 with an inclinationangle of γ=55 degrees emits light onto the reflective-type liquidcrystal display panel having a diffusion action of approximately 25degrees, the emission light becomes maximum in a perpendicular axisdirection of the liquid crystal display panel, obtaining the optimallight emission direction. On the other hand, in case the inclinationangle γ goes out of a range of 45-65 degrees, light emission becomesunavailable in a direction perpendicular to the light emission surface44 b (z-axis direction), thus requiring a prism sheet or the like.Therefore, the deflecting slant surface 46 a of the diffusion pattern 46preferably has an inclination angle γ magnitude of in the range of 45-65degrees.

[0200] Next, consideration will be made on an angle δ of the rearsurface 46 b of the diffusion pattern 46. As in FIG. 39, in case theangle δ of the rear surface 46 b is excessively small, the diffusionpattern 46 is in a saw-tooth form. Accordingly, the light, transmittedthrough the deflecting slant surface 46 a of the diffusion pattern 46and again entered at the rear surface 46 b, is incident on the lightemitting surface 44 b before striking a diffusion pattern 46 in the rearand emitted along the light emitting surface 44 b, thus resulting in aloss. For this reason, the angle δ of the rear surface 46 b ispreferably great, preferably at least greater than the inclination angleγ of the deflecting slant surface 46 a (γ<δ).

[0201] Meanwhile, as shown in FIG. 40, in case the angle δ of the rearsurface 46 b is small, the light transmitted through the deflectingslant surface 46 a is readily to leak out of the light conductor plate46. However, as shown by the broken line in FIG. 40, as the angle δ ofthe rear surface 46 b nears to 90 degrees, there is increase in theratio of light to be re-incident on the rear surface 46 b. On the otherhand, at an angle exceeding 90 degrees, it is impossible to form a lightconductor plate 44. Accordingly, the angle δ of the rear surface 46 b ispreferably in a range of 80-90 degrees as a measure, furthermoredesirably 85-90 degrees.

[0202] Incidentally, FIGS. 41 (a) (b) (c) shows a structure of aconventional light emitting part. There have been three light-emittingpart structures, i.e. (i) a structure as shown in FIG. 41(a) that a spotlight source 53, such as a light-emitting diode, is converted into alinear light source by a light conductor 54 and then spread into aplanar form, (ii) a structure as shown in FIG. 41(b) that spot lightsources 53 are arranged at an equal interval to provide a linear lightsource in a false fashion to spread the light thereof into a planarform, (iii) a structure as shown in FIG. 41(c) that the light emittedfrom a spot light source 48 is directly spread into a planar form.

[0203] In order to improve the directivity at each point on a lightconductor plate 55 as viewed at the upper surface of the light conductorplate 55, realization is relatively easy by the structure (iii). In thiscase, however, there is increase in the amount of light leaking at thepoints P2, P3 in FIG. 41 in a side surface of the light conductor plate55, thus raising a problem that efficiency is difficult to increaseMeanwhile, at a corner P1 of the light conductor plate 55 the requiredamount of light is extremely great as compared to that at the point ofP2 or P3. On the contrary, it is actually difficult to increase theamount of light to be conducted toward P1 as compared to that of P2, P3.For this reason, actually the amount of leak light at the point of P2,P3 must be increased to match the brightness at P2, P3 with thebrightness at the point of P1 thereby equalizing the brightness. Thus,the leak amount of light is increased at P2 and P3, thereby loweringefficiency.

[0204] Contrary to this, in the structure as in (i) (ii), notice hasbeen paid only to equalizing the brightness in a plane withoutconsideration for improving the directivity of the light to be emittedfrom the light conductor plate 55. In particular, the point of makingeven the brightness of the light emitted from the light conductor plate55 in a range of ±10-30 degrees, not seen in any of (i) (ii) (iii), isunique to the present invention.

[0205] (Second Preferred Embodiment)

[0206] Next, explanation will be made on a case with a surface lightsource device 56 of a front light type. In this case, a light conductorplate 44 is provided on an upper surface of a reflective-type liquidcrystal display panel 57, as shown in FIG. 42. A light emitting surface44 b is positioned in a lower surface of the light conductor plate 44. Alight emitting part 45 converts the light emitted from a spot lightsource, such as a light-emitting diode, into a linear form, and causesit to be incident at a light incident surface 44 a on the lightconductor plate 44. Consequently, the light incident on the lightconductor plate 44, upon being totally reflected upon the lightconductor plate 46, is emitted at a light emitting surface 44 b towardthe direct below, thereby lighting a reflective-type liquid crystaldisplay panel 57 placed below a surface light source device 53. Thelight reflected by the reflective-type liquid crystal display panel 57returns again into the light conductor plate 44 and emitted upwardthrough between the light conductor plates 46.

[0207] For the surface light source device 56 for use as a front lightin this manner, in case roundness occurs at an apex of a triangulardiffusion pattern 46 or at a boundary between a back surface 46 b and alower surface as shown in FIG. 43, the light directly emits toward anobserver, thus lowering the contrast of the light including an imagereflected by the reflective-type liquid crystal display panel 54.Consequently, these points preferably have a smaller radius of curvatureR1, R2. However, in case the radius of curvature R1, R2 is made small bya mold die for forming a light conductor plate 46, there is a fear tocause roundness during forming. This is not preferred because of causingvariation between the individuals or variation depending upon a positiondue to a delicate forming condition (e.g. resin lot variation, etc.).Consequently, in order to suppress the variation, a small amount ofradius of curvature is preferably provided on the mold die from thebeginning. From a forming limit, R1, R2 is 0.25 μm or greater. Also, inorder to suppress the lower of contrast, this is preferably one-third orsmaller, further more preferably one-fifth, of a height T of thediffusion pattern 46.

[0208] (Third Preferred Embodiment)

[0209]FIG. 44 is a plan view showing a structure of a surface lightsource device 58 according to a third preferred embodiment of theinvention. This embodiment is characterized in that diffusion patterns46 do not extend over the entire length of the light conductor plate 44but the diffusion patterns 46 short in length are distributed entirelyon the light conductor plate 44 unlike the first embodiment. On thecloser side to the light emitting part 45, the diffusion patterns 46have a small distribution density. As distant from the light emittingpart 45, the diffusion patterns 46 are increased in distributiondensity. By thus distributing the shortened diffusion patterns 46, thereis increase in freedom of arranging the distribution patterns 46.Accordingly, it is possible to make even the brightness distribution ofthe light emitted from the light conductor plate 44.

[0210] As shown in a comparative explanatory view of FIG. 45, in thecase that the emission light from the light emitting surface 44 b has anintense directivity in the x-axis direction but spread in the y-axisdirection, in order to spread the directivity in the x-axis directionthere is a need to arrange, for example, a weak diffusion plate on thelight conductor plate 44 thereby causing diffusion in the emission lightand spreading the directivity in the x-axis direction. Thus, thereencounters size increase as a surface light source device.

[0211] For this reason, in the embodiment of FIG. 44, the diffusionpattern 59 for causing somewhat diffusion of light in the x-axisdirection is provided on the light incident surface 44 a of the lightconductor plate 44 thereby adjusting nearly equal the directivity in thex-axis direction and the directivity in the y-axis direction. Thediffusion pattern 59 can use, for example, a prism-formed pattern. Asdescribed before, emission light preferably has a directivity of atleast 10 degrees or greater. Accordingly, in the case that thedirectivity in the x-axis direction is smaller than 10 degrees, the useof such means can provide a directivity in the x-axis direction ofapproximately 10 degrees or greater.

[0212] (Fourth Preferred Embodiment)

[0213] Meanwhile, the surface light source device 60 shown in FIG. 46 ismade to broaden the light directivity in the x-axis direction by thediffusion patterns 46. Namely, in also this surface light source device60, short diffusion patterns 46 are distributed entirely on the lightconductor plate 44. The diffusion pattern 46 is not in a straight-lineform but moderately winding along a lengthwise direction as shown inFIG. 47. Accordingly, depending on a position on the diffusion pattern46, there is slight difference in the reflecting direction of incidentlight. Thus, emission light can be broadened also in a directionorthogonal to a direction of light's traveling. For example, in the casethat the maximum angle defined by a tangent line drawn on the diffusionpattern 46 and an x-axis direction is ?=13 degrees, the light reflectedupon the diffusion pattern 46 can be broadened in directivity byapproximately ?20 degrees.

[0214] Meanwhile, even where there is no winding in the individualdiffusion pattern 46 itself, in case the diffusion patterns 46 aredirected in different directions as shown in FIG. 48, it is possible toobtain an effect to totally broaden the directivity of emission light.

[0215] The directivity is different, for a diffusion pattern 46 as inFIG. 47, depending upon in which position of the diffusion pattern 46the maximum tangential angle is and, for a diffusion pattern 46 as inFIG. 48, depending upon which diffusion pattern 46 is inclined greatest.However, the emission-light angular distribution can be made even forthe diffusion pattern 46 as in FIG. 47 by designing such that theinclination of each part exists at a constant ratio of from the maximumvalue to 0, and for the diffusion pattern 46 as in FIG. 48 by designingsuch that the inclination of each diffusion pattern 46 distributesnearly evenly. Meanwhile, by eliminating the region perpendicular to adirection of light s traveling in plan view or each diffusion pattern 46or by reducing the ratio, it is possible to lower the brightness in adirection perpendicular to the light emitting surface.

[0216] Now, by totally reflecting the light having a directivityextremely narrow in the x-axis direction in the light conductor plate 44(FIG. 23(a)) by such a diffusion pattern 46 as in FIG. 47, considered isto realize an ideal light conductor plate light emission angulardistribution. The ideal light conductor plate light emission angulardistribution preferably has an emission light intensity lying constantin a certain range and zero in the other as mentioned above. In the casethat the light traveling inside the light conductor plate 44 isunidirectionally aligned as viewed in the z-axis direction, realizationis possible by winding the diffusion pattern 46 as in FIG. 47.Considered is the light L4, L5, L6 which strikes e-part, f-part, g-partof a diffusion pattern 46 winding in an S-form to be totally reflectedand emitted at a light emitting surface 44 b as shown in FIG. 49. Forthe light L4 striking the e-part, because the diffusion pattern 46 inplan view is perpendicular, the light L4 totally reflected is emittedonto the z, y plane as shown in FIG. 50. A view viewed from the z-axisis shown in FIG. 51(a). In FIG. 51(a), the reflected light L4 isparallel with the y-axis.

[0217] Contrary to this, of the totally reflecting light L5, L6 due tostriking the f-part and g-part of the diffusion pattern 46, the lightreflected in a minus direction on the y-axis goes away from the light ofL4 while the light reflected in a plus direction on the y-axis goes nearthe light of L4. Specifically, of the light L6 reflected at a g-point,the light reflected in the minus direction on the y-axis as the ray C1shown in FIG. 51(b) has a great deflection angle upon reflection by thediffusion pattern 46 to travel greatly distant from the light of L4.However, the light reflected in the plus direction on the y-axis as theray C2 has a small deflecting angle upon reflection by the diffusionpattern 46 not to travel greatly distant from the light of L4.Consequently, the light L5, L6 reflected at the f-point or g-point, asviewed in the z-axis direction, is spread in a direction shown in FIG.51(a) and emitted. Accordingly, in case light is reflected between thef-point and the g-point of the diffusion pattern 46 as represented inFIG. 49, it after emission in the z-axis direction is spread in a regionbetween the light L5 and L6 shown in FIG. 51(a).

[0218] Meanwhile, when light is incident nearly parallel with thedeflecting slant surface 46 a as viewed in the x-axis direction, thelight L4 and L6 coincide. As the angle to the deflecting slant angle 46a increases, the light L4 and L6 go distant farer. Consequently, as theangle to the deflecting slant surface 46 a increases, the amount oflight per unit angle in the x-axis direction decreases. However, asnoted before, considering only the ray on L4, L5 or L6, essentially theamount of light to be reflected upon the diffusion pattern 46 becomeszero in intensity when the light is nearly in parallel with thedeflecting slant surface 46 a of the diffusion pattern 46, wherein theamount of reflection light increases with increase of the angle to thedeflecting slant surface 46 a. As a result of offset of these twoeffects, the light is even in a region surrounded by A1, B1, B2, A2, C2and C1, i.e. in an angle range the light is to be emitted. In thisdirectivity characteristic, the light emission angle is −22 to +37degrees in the y-axis direction and the light emission angle is −25 to+25 degrees in the x-axis direction. Accordingly, Δθy=59 degrees andΔθx=50 degrees is given, in which range nearly 100% of light is to beemitted.

[0219] Incidentally, even where the diffusion pattern 46 winds,direction of light's traveling is made almost not changed before andafter the transmission through the diffusion pattern 46 of the lighttransmitted through the deflecting slant surface 46 a of the diffusionpattern 46 and re-incident at the back surface 46 b as viewed in adirection perpendicular to the light incident surface 44 a. For this, incase the deflecting slant surface 46 a and the back surface 46 b aremade parallel with each other as viewed in a direction perpendicular tothe light incident surface 44 a, direction of light's traveling isnearly the same before and after transmission through the diffusionpattern 46.

[0220] (Fifth Preferred Embodiment)

[0221]FIG. 53 shows a surface light source device 61 according to afifth preferred embodiment of the invention to be used as a backlight.This surface light source device 61 has a regular reflection plate 62arranged parallel with a back surface of a wedge-formed light conductorplate 44 and a prism sheet 63 opposed to a light emitting surface 44 bof the light conductor plate 44. The wedge-formed light conductor plate44 is made with a slant surface in its back surface, the inclination ofwhich is η=1.52 degrees, for example. Meanwhile, the light conductorplate has a size, for example, having a length of 30 mm, a thickness ofa light incident surface 44 a of 1 mm and a thickness at a tip of 0.2mm. The light conductor plate 44 thus made is seen as if there were nodiffusion patterns 46 at a first glance. However, it can be consideredthat the back surface and the light incident surface 44 a are notparallel, and the lower surface entirety is made as one diffusionpattern 46. In the showing in FIG. 53, a prism sheet 63 arranged withprisms having an apex angle of 40 degrees or greater is arranged withits pattern surface directed outward. The pattern surface may be opposedto the light incident surface 44 a of the light conductor plate 44. Insuch a case, the prism apex angle is not limited to 40 degrees. Also, alight emitting part 45 is to convert the light of a spot light source,such as a light-emitting diode, into a linear light source and emit it.This can use, for example, a light emitting part 45 as was explained inthe first embodiment formed by a wedge-formed light conductor 47, a spotlight source 48, a regular reflection plate 49 and a prism sheet 50.Incidentally, the back surface of the light conductor plate 44 may becurved instead of a flat surface.

[0222] Then, the light emitted from the light emitting part 45 andincident at the light incident surface 44 a on the light conductor plate44, each time striking the back surface (diffusion pattern 46) to bereflected, gradually decreases in the incident angle on the lightemitting surface 44 b or back surface. When the incident angle on thelight incident surface 44 a exceeds a critical angle of totalreflection, the light is emitted at the light emitting surface 44 b.Meanwhile, as shown in FIG. 54, the light emitted at the back surface ofthe light conductor plate 44 is regularly reflected without diffusion bythe regular reflection plate 62, and re-incident again on the lightconductor plate 44 without change in light direction. The light emittedat the light emitting surface 44 b is emitted along the light emittingsurface 44 b as shown in FIG. 54 and then deflected by the prism sheet63, to be emitted in a direction perpendicular to the light emittingsurface 44 b.

[0223] Herein, concerning the light emitted from the light conductorplate 44, the major part of light is emitted along the y-axis as viewedin the x-direction (or viewed by projection on the y-z plane). There isa concentration of 99% of light in the angle defined with the lightemitting surface 44 b, ρ=0-40 degrees. Consequently, concerning thelight angularly deflected by the prism sheet 63, the major part of lightconcentrates in a range of ±20 degrees with respect to the z-axisperpendicular to the light emitting surface 44 b of the light conductorplate 44 as viewed in the x-axis direction.

[0224] Meanwhile, with the light emitting part 45 as explained in thefirst embodiment, the light emitted from the light emitting part 45concentrates 80% or more of light in a range of ±13 degrees with respectto the y-axis as viewed in the z-axis direction. Consequently, theemission light from the light conductor plate 44 also concentrates 80%or more in a range of ±20 degrees with respect to the z-axis as viewedin the y-axis direction.

[0225] Accordingly, the emission light from the prism sheet 63 isemitted nearly parallel with the z-axis without spread in the x-axisdirection and y-axis direction, thus obtaining an extremely highdirectivity.

[0226] Meanwhile, the reflection plate for reflecting leak light needsto use a regular reflection plate 62. It is needless to say that highdirectivity is not obtained by a diffusion type reflection plate. Theregular reflection quality and reflective index of this regularreflection plate 62 has an effect upon the amount of light to be emittednearly parallel with the light emitting surface. It is desired to use aregular reflection plate 62 to emit, at the light emitting surface 44 b,at least two-thirds of light in an angle range of ρ=0-40 degrees. Incase such an amount of light is emitted at the light emitting surface 44b, it is possible to emit 50% or more of light in the z-axis directionafter transmission through the prism sheet 63. FIG. 55 and FIG. 56represent intensity angle characteristics of the light emitted from thelight conductor plate 44, respectively, for the case using a diffusiontype reflection plate on the back surf ace of the light conductor plate44 and the case using a regular reflection plate. It can be seen fromthe measurement data that the major part of light is contained in arange of ρ=0-30 degrees for the case using the regular reflection plate62 whereas the considerable part of light is emitted into a range ofρ≧30 degrees for the case using the diffuse-reflection plate.

[0227] The light conductor plate 44 used in this embodiment is notlimited to a wedge form in a section but may be provided, for example,with a prism-formed pattern 64 on the back surface as shown in FIG. 57.In the case with this light conductor plate 44, the inclination angle γof the prism-formed pattern 64 on the back surface, if given 10 degreesor smaller, obtains a directivity equivalent to the wedge-formed lightconductor plate 44. Nevertheless, the inclination angle γ is preferably5 degrees or smaller, particularly desirably 2 degrees or greater and 5degrees or smaller. Meanwhile, the inclination angle γ of the prismpattern 64 is not necessarily even but may be given such that theinclination angle γ is relatively small on a light incident surface sideand increased as going toward the tip.

[0228] Furthermore, similarly to the light conductor plate 44 shown inFIG. 58, a prism-formed pattern 64 may be provided only at aback-surface tip of a wedge-formed plate. Herein, the inclination angleγs of the prism-formed pattern 64 is given greater than the inclinationangle γ of the wedge-like part, e.g. γ=2 degrees and γs=3 degrees.

[0229] Meanwhile, the light emitting part 45 is not limited to thestructure as explained in the first embodiment. However, as shown inFIG. 59, a plurality of spot light sources 65, such as light-emittingdiodes, merely opposed to the light emitting surface 44 b of the lightconductor plate 44 provides, at a glance, a high directivity but muchleak light in sideway direction, which in many cases is improper.Otherwise, in case the light flying sideways is to be bent parallel withthey-axis direction, there encounters size increase in the z-axisdirection. For this reason, it in many cases cannot be used as it is.

[0230] For this reason, similarly to the light emitting part shown inFIG. 60 for example, a cylindrical lens 66 is placed between the spotlight sources 65 and the light conductor plate 44 to restrict light inthe z-axis direction by the cylindrical lens 66.

[0231] Also, as shown in FIG. 61, spot light sources 65, such aslight-emitting diodes, maybe arranged in plurality to provide concavemirrors 67 covering at the back thereof. With such a light-emitting part45, light is emitted from the spot light source 65 toward the concavemirror 67 to cause the nearly collimated light, due to reflection uponthe concave mirror 67, to be incident on the light conductor plate 44.

[0232] (Sixth Preferred Embodiment)

[0233]FIG. 62 is a plan view showing a structure of a surface lightsource device 68 according to a sixth preferred embodiment of theinvention. The light conductor plate 44 used in this surface lightsource device 68 has a light non-emitting region 44 d provided around alight-emitting region 44 c in a rectangular form for use as a lightsource. At an end of a shorter side of the generally rectangular lightconductor plate 44 and at the outside of the light-emitting region 44 c,a spot light source 48 using a diode is accommodated to integrallystructure a light emitting part 45. Meanwhile, the diffusion patterns 46sectionally in a triangular form, comprising a deflecting slant surface46 a and a rear surface (light re-incident surface) 4 b, are arranged onconcentric circles about the spot light source 48. The interval of thediffusion patterns 46 is relatively broad on a side close to the spotlight source 48 (pattern density may be constant in a region extremelyclose to the spot light source). The spacing is shortened as distantfrom the spot light source 48. This provides even brightness over thelight emitting surface 44 b. Meanwhile, in the case of using two or morelight-emitting diodes, pluralities of light-emitting diodes are gatheredat one point thereby making a spot light source. Note that, in FIG. 62,69 is a film wiring board (FPC) to feed power to the spot light source48.

[0234] The diffusion patterns 46 are arranged such that the lengthwisedirection thereof is nearly orthogonal to a direction connecting to thespot light source 48. The light totally reflected by the diffusionpattern 46 is emitted in a direction nearly perpendicular to the lightemitting surface 44 b. The light transmitting the diffusion pattern 46transmits through it without significant change in traveling direction.Accordingly, the direction of a ray at each point is unidirectionallyaligned at each point as viewed from the direct above the lightconductor plate 44. Consequently, as viewed in a direction perpendicularto the light emitting surface 44 b, the light emitted from the spotlight source 48 travels radially without being scattered sideways. Thelight totally reflected by the diffusion patterns 46 is allowed to emitat the light emitting surface 44 b.

[0235] The surface light source device 68 like this can be used as abacklight placed on a back surface of a transmission-type liquid crystaldisplay panel 70, as shown in FIG. 63. In such a case, although noreflection plate may be provided on the back surface of the lightconductor plate 44, a reflection plate 69, such as a regular reflectionplate or diffuse-reflection plate, may be provided on the back surfaceof the light conductor plate 44 as shown in FIG. 63. However, in thecase of using a diffusion plate on the back surface of the lightconductor plate 44 (particularly, in the case the spot light source 48has a narrow directivity), there is a need to use one sufficiently smallin diffusive action in order not to adversely impair the directivity.

[0236] Also, the surface light source device 68 like this can be placedin front of a reflective-type liquid crystal display panel 71 and usedas a front light, as shown in FIG. 64. In this case, anti-reflectionfilms 72 are provided on the both surfaces of the light conductor plate44 thereby improving light utilization efficiency, as shown in FIG. 64.

[0237] FIGS. 65(a) (b) is a plan view and magnifying sectional viewshowing a form of the diffusion pattern 46. The diffusion pattern 46 hasa nearly uniform section in a lengthwise direction and arrangedperpendicular to a ray traveling direction. Meanwhile, the diffusionpattern 46 used herein somewhat winds similarly to that of FIG. 65(a).The diffusion pattern 46 is formed nearly in a rectangular triangularform by a deflecting slant surface 46 a and a rear surface 46 b. Theinclination angle γ of the deflecting slant surface 46 a and theinclination angle δ of the rear surface 46 b are desirably given as

γ<δ,

γ=45°-65°

δ=80°-90°.

[0238] In the case of using, for example, a light conductor plate 44 ofa transparent resin having a refractive index n=1.53, when thedeflecting slant surface 46 a has an inclination angle γ=55° as shown inFIG. 66, the emission light from the light conductor plate 44 is emittedin a range of −25°-+35° as viewed in the x-axis direction. This is areflection upon the diffusion pattern 46 of the light striking thediffusion pattern 46 from the below. The light striking from the aboveis again incident at the rear surface (light re-incident slant surface)46 b on the light conductor plate 44, as shown in FIG. 67.

[0239] Meanwhile, FIGS. 68(a) (b) (c) (d) represents a manner ofarranging the entire diffusion patterns 46. FIG. 69 shows a patterndensity (area ratio) change in a radial direction. FIG. 70 shows apattern length change. FIG. 71 shows a change in the number of patternsper unit area. r represents a distance from the light emitting part 45.The diffusion patterns 46 increases the density with the increase in thedistance from the light emitting part 45, as shown in FIG. 69. This isbecause to make even the brightness on the light emitting surface 44 b.For the method for gradually increasing the diffusion pattern density,it is possible to gradually increase the number of diffusion patternsper unit area. In this embodiment, however, the light conductor plate 44is divided into a plurality of doughnut-formed zones in accordance witha distance from the light emitting part 45. Each zone has therein aconstant number of diffusion patterns per unit area, as shown in FIG.71. Furthermore, the number of diffusion patterns per unit area isincreased stepwise based on each zone. As shown in FIG. 70, in eachzone, the length of the diffusion pattern is gradually changed.Meanwhile, at a zone boundary, the pattern length is once shortened.

[0240] FIGS. 68(b) (c) (d) concretely represents the diffusion patternsrespectively in the points of A, B and C of FIG. 68(a). In FIG. 68(b),both the radial pitch and the circumferential pitch of diffusionpatterns 46 are 140 μm in a region A closest to the light emitting part45, thereby preventing against the radial overlap between the innerdiffusion pattern 46 and the outer diffusion pattern 46. FIG. 68(c) isan intermediate region B, wherein both the radial pitch and thecircumferential pitch of diffusion patterns 46 are 70 μm. The innerdiffusion patterns 46 and the outer diffusion patterns 46 are overlappedby each two rows. FIG. 68(d) is a distant region C from the lightemitting part 45, wherein the radial pitch is 35 μm and thecircumferential pitch is 140 μm. Incidentally, although FIGS. 68(b) (c)(d) illustrated the diffusion patterns extending in a straight-lineform, the winding diffusion patterns shown in FIG. 65 may be arranged asin FIGS. 68(b) (c) (d).

[0241] Meanwhile, the longer side of the light conductor plate, on aside opposite to an end the light emitting part 45 is arranged, isformed straight whereas the longer side of the light conductor plate ona side close to the light emitting part 45 is cut obliquely by one or aplurality of stages. Similarly, close to the light emitting part 45, theshorter side is formed oblique in part thereof. In case slant surfaces73, 74 are provided respectively on a longer side and shorter side closeto the light emitting part 45, as shown in FIG. 72, part of the lightemitted from the light emitting part 45 is totally reflected at thelonger-side slant surface part 73 and shorter-side slant surface part 74to send light to the corners of the light conductor plate 44 (hatchedregions in FIG. 72). In the case that the light emitting part 45 isplaced at a corner of the light conductor plate 44, the other cornerslikely to be dark. With this structure, however, the light totallyreflected upon the slant surface parts 73, 74 is sent to the corners ofthe light-emitting region 44 c of the light conductor plate 44, therebymaking more even the brightness distribution on the surface light sourcedevice 68 and enhancing the efficiency of the surface light sourcedevice 68.

[0242] Incidentally, where a fixing frame 75 is attached on the lightconductor plate 44 as shown in FIG. 73, if the structure is made with aclose contact between the slant surface parts 73, 74 for lightreflection and the fixing frame 75, the slant surface parts 73, 74 ofthe light conductor plate 44 are ready to be scratched causing a fear toimpair reflection characteristic. In order to prevent this, a smallconvex-formed projection 76 is provided in one part of thelight-reflecting slant surface part 73, 74 or in the vicinity thereof.It is preferred that the light conductor plate 44 is in contact with thefixing frame 75 through the convex-formed projection 76 while a gap isprovided between the slant surface part 73, 74 and the fixing frame 75.

[0243] Next, explanation will be made on an anti-reflection film 72. Inthe case of using the surface light source device 68 as a front light,it is possible to prevent shine by providing an anti-reflection film (ARcoat) 72 for prevent shine (the light of other than an image, e.g.bright shine with reflection light preventing from viewing an image) onthe both surfaces of the light conductor plate 44 or on the surfaceformed with diffusion patterns 46. However, the anti-reflection film 72is to prevent the shine caused by reflection of external light upon asurface (planar part 44 e) of the light conductor plate 44, as shown inFIG. 74. This light is incident perpendicularly on the planar part 44 eof the light conductor plate 44. Contrary to this, the light of thelight emitting part 45 transmitted through the deflecting slant surface46 a is obliquely incident on a round part 44 f at the boundary betweenthe rear surface 46 b and the planar part 44 e of the diffusion pattern46 as shown in FIG. 74, thereby to be reflected as shine toward anobserver.

[0244] However, in case an anti-reflection film 72 is formed in an eventhickness in a manner suppressing the shine due to external light, thereis less effect on the light obliquely incident on the anti-reflectionfilm 72 similarly to the light of from the light emitting part 45obliquely incident on the round part 44 f at the boundary between therear surface 46 b and the planar part 44 e of the diffusion pattern 46.As shown in FIG. 75, provided that the light emitted from the lightemitting part 45 has a wavelength (light-source wavelength) ofapproximately 450 nm, the anti-reflection film 72 for use is designedsuch that reflective index is the minimum at the relevant wavelength asshown in FIG. 76. When light is incident obliquely to shorten aconversion wavelength, there is increase in reflective index.Consequently, in order to prevent such shine due to the light of fromthe light emitting part 45, it is effective to partially increase thefilm thickness of the anti-reflection film 72 in a round part 44 f atthe boundary between the rear surface 46 b and the planar part 44 e ofthe diffusion pattern 46.

[0245] In order to partially increase the film thickness of theanti-reflection film 72 in the round part 44 f at an end of thediffusion pattern 46 in this manner, the light conductor plate 44 isobliquely placed within a vacuum evaporation apparatus 77 forevaporating an anti-reflection film 72, as shown for example in FIG. 77.This can be easily carried out by placing the round part 44 f directlyfacing to an evaporation source 78. Because the anti-reflection film 72to be evaporated on an inclined part is reduced in thickness, it ispossible to increase the film thickness at the round part 44 f than theother by evaporating an anti-reflection film 72 in a state the lightconductor film 44 is inclined.

[0246] Meanwhile, as shown in FIG. 78, the shine on the planar surface44 e at close to the diffusion pattern of the light conductor plate 44is due mainly to external light. On the contrary, the shine on the lightemitting surface 44 b of the light conductor plate 44, as shown in FIG.78, is due to the light L11 of from the light emitting part 45 that hasbeen reflected upon the deflecting slant surface 46 a and furtherreflected upon the light emitting surface 44 b. These are noises againstan image given by the light L12 of from the light emitting part 45 thathas been reflected upon the deflecting slant surface 46 a and furtherupon the reflective-type liquid crystal display panel 71. Accordingly,in order to prevent the shine due to the light reflected upon the bothsurfaces of the light conductor plate 44, a usual anti-reflection film72 (or an anti-reflection film 72 partly increased in film thickness asin the above) may be formed on the planar part 44 e in the surface on aside formed with the diffusion patterns 46 while, on the light emittingsurface 44 b may be used an anti-reflection film 79 specific for thelight of from the light emitting part 45.

[0247] However, because a white light-emitting diode usually having twopeaks (450 nm, 550 nm on its wavelength spectrum as shown in FIG. 79,there is a need to suppress reflective index at the two peaks. The lightL11 reflected upon the light emitting surface 44 b has a somewhat widthfor the anti-reflection film 79. For the oblique incident light, thereflective-index characteristic of the anti-reflection film 79, in manycases, deviates toward a lower wavelength side than that ofperpendicular incident light. For this reason, the anti-reflection film79 for use on the back side preferably has a visible range of reflectiveindex having two minimum values, wherein the spacing between the twominimum values is broader than an interval of the peaks in the lightemitted from the spot light source 48. Furthermore, it is more preferredthat the two average values of the reflective-index minimum values ofthe anti-reflection film 79 are longer in wavelength than an averagevalue of the two peaks of the spot light source 48.

[0248]FIG. 80 is a sectional view showing a structure of a lightemitting part 45 buried at an end of a shorter side of the lightconductor plate 44. The light emitting part 45 has a light-emittingdiode chip 81 sealed in a transparent resin 82 and covered with a whitetransparent resin 83 at the surfaces other than the front surfacethereof. The light emitting part 45 is mounted on a film wiring board 84and fixed by a solder 85. Furthermore, the film wiring board 84 is fixedon a reinforcing plate 86 formed of a glass epoxy resin. The lightconductor plate 44 has a light-source mounting part 87 perpendicularlypenetrated with a hole 88 for accommodating the light emitting part 45.In the vicinity of the light-source mounting part 87, a positioning pin89 projects on a lower surface of the light conductor plate 44. On theother hand, a through-hole 90, 91 is opened, for passing the positioningpin 89, in the film wiring board 84 and reinforcing plate 86.

[0249] Then, a ultraviolet cure type adhesive (thermo-set type adhesivealso usable) 92 is previously applied to a lower surface of the lightconductor plate 44, at around abase of the positioning pin 89. Thepositioning pin 89 is inserted through the through-hole 90, 91 of thefilm wiring board 84 and reinforcing plate 86, to make a positioning ofa thick-wise center of the light conductor plate 44 and a light-emittingcenter of the light emitting part 45 by a CCD camera or the like.Thereafter, a ultraviolet ray is radiated to cure the ultraviolet curetype adhesive 92 thereby bonding between the light conductor plate 44and the light emitting part 45. Furthermore, the positioning pin 89 isthermally fitted with the reinforcing plate 86.

[0250] At this time, as shown in FIG. 80, the light emitting part 45 atits center may be positioned by the projection 93 provided in an innersurface of the hole 88 of the light-source mounting part 87 (rearsurface side of the light emitting part 45, front surface side or boththereof may be used). Meanwhile, although not shown, in a state thelight conductor plate 44 and the light emitting part 45 areperpendicularly inverted, a center of the light conductor plate 44 and acenter of the light emitting part 45 are aligned by the use of a jighaving a step for positioning an upper surface of the light conductorplate 44 and an upper surface of the light emitting part 45. Meanwhile,a glass epoxy wiring board or a leadframe may be used in place of thefilm wiring board 84.

[0251] The light conductor plate 44 thus mounted with the light emittingpart 45, e.g. for a transmission type liquid crystal display device, ismounted, with the reinforcing plate 86 side positioned up (or may bepositioned down), on a main board 94, as shown in FIG. 81. The filmwiring board 84 at its end is connected to a heat sink 96. Furthermore,a transmission type liquid crystal display panel 70 is superposed on thelight conductor plate 44. The end of the film wiring board 97 connectedto the liquid crystal display panel 70 is also fixed to the heat sink 98on the main board 94.

[0252] When forming a rectangular light conductor plate 44 as notedabove, in case such a rectangular light conductor plate 44 is to beformed directly, there occurs uneven flow of the resin within a mold die98, as shown in FIG. 82. It is difficult to achieve a pattern transfereven over the entire surface, thus readily causing warp in the lightconductor plate. However, as shown in FIG. 83, a mold die 98 is madesomewhat greater than a light conductor plate 44 to be made. The molddie 98 is used to make a fan-shaped or semicircular light conductorplate 99 having a somewhat greater size. By properly cutting it, a lightconductor plate 44 can be formed. In this manner, in case a somewhatgreater light conductor plate 99 having a favorable resin fluidity isformed and then cut thereby fabricating a desired light conductor plate44, resin fluidity is even in every direction during forming a somewhatgreater light conductor plate 99. Thus, it is possible to achievepattern transfer even over the entire surface. and reduce the occurrenceof warp in the light conductor plate 44.

[0253] Incidentally, mentioning a size of the surface light sourcedevice shown in FIG. 62, the length in a shorter side direction of thelight conductor plate 44 is 33 mm, the length in a longer side directionis approximately 43 mm (approximately 47 mm if including a light-sourcemount part) and the thickness is 0.1 mm. Meanwhile, thenon-light-emitting region 44 d of the light conductor plate 44 has awidth of 0.2 mm. Furthermore, the light-emitting diode as a spot lightsource 48 has a width of approximately 25 mm and a depth of 1.3 mm.

[0254]FIG. 84 represents a cellular phone 100 built, as a display 101,with a reflection-side liquid crystal display unit using a surface lightsource device 68 structured as the above. The cellular phone 100 has aspeaker 102 and antenna 103 above the display 101, and an operationbutton (dials, etc.) 104 below the display 101. Meanwhile, FIG. 85represents a PDA 105 using, as a display 106, a surface light sourcedevice 68 structured similarly to the above. This PDA has operationbuttons 107 below the display 106.

[0255] In the cellular phone 100 or PDA 105, the liquid crystal displayscreen of the display 101, 106 in many cases uses fully the frontsurface of the apparatus. Also, it is long in the longitudinal directionand narrow in width. Also, in the above and below the display 101, 106,provided in many cases are operation switches 104, 107, a speaker 102and the like. Consequently, as in the surface light source device 68mentioned above, the use of an arrangement of a light emitting part 45at an end close to a shorter side facilitates parts arrangement anddesign, contributing to the size reduction of the cellular phone 100 orPDA 105. Particularly, in the case of the cellular phone 100, becausethe antenna 103 causes electromagnetic waves at high frequency, an IC,radio frequency circuit or the like cannot be placed in the vicinitythereof. However, because a spot light source, such as a light-emittingdiode, is less susceptible to the effect of radio-frequencyelectromagnetic wave, placing a light emitting part 45 herein can makeeffective use of space.

[0256] (Seventh Preferred Embodiment)

[0257]FIG. 86 is a figure showing the characteristic of a liquid crystaldisplay unit using, as a front light, a surface light source deviceaccording to a seventh preferred embodiment of the invention. FIG. 86(A)is a figure showing an emission-light intensity angular distribution ofthe light emitted from the light conductor plate 44, showing a nearlyflat characteristic. FIGS. 86(B)-(E), in any, are characteristicscorresponding to the emission-light intensity angular distribution ofthe same FIG. (A). FIG. 86(B) shows an intensity distribution of thelight reflected upon the lower surface of the light conductor plate 44and emitted at the light emitting surface 44 b. FIG. 86(C) shows adiffusion characteristic of the liquid crystal display panel. FIG. 86(D)shows an emission-light intensity characteristic of from the liquidcrystal display panel. FIG. 86 (E) shows an S/N ratio upon lighting ofthe surface light source, which is a ratio of an image emitted towardthe front after reflection upon the liquid crystal display panel [sameFIG. (D) ] and a noise light emitted toward the front due to reflectionupon the lower surface of the light conductor plate 44 [same FIG. (B)](see FIG. 78).

[0258] Similarly, FIG. 86(a) is a figure showing an emission-lightintensity angular distribution of the light emitted from the lightconductor plate 44, showing a characteristic recessed at nearly thecenter. FIGS. 86(b)-(e), in any, are characteristics corresponding tothe emission-light intensity characteristics of the same FIG. (a). FIG.86(b) shows an intensity distribution of the light reflected upon thelight conductor plate 44. FIG. 86(c) shows a diffusion characteristic ofthe liquid crystal display panel. FIG. 86(d) shows an emission-lightintensity characteristic of from the liquid crystal display panel. FIG.86(e) shows an S/N ratio.

[0259] The contrast during surface light-source lighting of the liquidcrystal display unit (without external light) is determined by S/N ofthe reflection light (image) from the reflective-type liquid crystaldisplay panel and reflection light (shine) due to the light conductorplate 44. However, the characteristic FIG. [86(B), (b)] of the lightemitted after reflection upon the light conductor plate 44 issusceptible to the effect of an emission-light intensity angulardistribution of the light emitted from the light conductor plate 44whereas the mage reflected upon the liquid crystal display panel [FIG.86(D), (d)] is less susceptible to the effect of an emission-lightintensity angular distribution of the light emitted from the lightconductor plate 44, wherein the characteristic is less changed where thespread thereof is somewhat changed by the diffusion characteristic ofthe liquid crystal display panel.

[0260] Accordingly, as shown in FIG. 86 (a)-(e), the S/N in aperpendicular direction can be raised by lowering the intensity of thelight emitted perpendicularly to the light emitting surface 44 b of thelight conductor plate 44.

[0261]FIG. 87 is a plan view showing one example of a diffusion pattern46 for realizing the characteristics as shown in FIG. 86(a)-(e). In thisdiffusion pattern 46, provided that the angle defined by the tangentialline thereof relative to a direction perpendicular to a direction oflight s traveling within the light conductor plate 44 is ν, the regionthis angle ν is nearly zero is given extremely small. Otherwise, it maybe completely eliminated. With a structure like this, it is possible toreduce the light to be emitted in a direction perpendicular to the lightemitting surface 44 b as viewed in a direction of light s traveling(y-axis direction), and to raise the S/N in the perpendicular direction.

[0262] (Eighth Preferred Embodiment)

[0263]FIG. 88(b) shows a surface light source device using a lightconductor plate having the same form of diffusion patterns throughoutthe entire thereof. With this surface light source device, the lightemitting direction at the light emitting surface 44 b is evenly alignedregardless of a position of light emission. When actually observing theliquid crystal display device, the angle of viewing it differs dependingon a position on the screen of the liquid display device. Consequently,in the case the directivity of the light conductor plate 44 is the sameregardless of a position, the brightness in view is different dependingon a pixel position resulting in an occurrence of uneven on-screenbrightness. Although this problem will be eliminated by providing aFresnel lens or the like on the light conductor plate 44, thereencounters the corresponding thickness increase of the surface lightsource device.

[0264] In such a case, the directivity may be varied in accordance withthe position by changing the shape (inclination angle γ of thedeflecting slant surface 46 a) and arrangement (lengthwise inclination νof the diffusion pattern 46) of the diffusion patterns 46 in accordancewith a position in the light conductor plate 44. Namely, as shown inFIG. 88(a), the diffusion patterns 46 are designed such that, in acenter region of the light conductor plate 44, light is emitted toward aperpendicular direction to the light emitting surface 44 b while, in aperipheral region, the direction of light emission at the light emittingsurface 44 b directs toward the center of the light conductor plate 44.By doing so, the diffusion patterns 46 can be provided with the functionof a Fresnel lens whereby the viewing at every position is at the samebrightness throughout the screen thus equalizing the brightness over thescreen entirety.

[0265] Industrial Applicability

[0266] The present invention is used as a surface light source devicefor use as a backlight or front light, and to be carried out inmanufacturing the surface light source device. The application is forwide fields of applications including liquid crystal display devices,and cellular phones and information terminals having liquid crystaldisplay devices in their display regions.

1. In a surface light source device having a light source and a lightconductor plate for spreading the light introduced from the light sourceto nearly entire of a light emitting surface and emitting it from thelight emitting surface, the surface light source device characterized inthat: 50% or more of the light emitted from the light conductor plate isemitted within an area defined by angles of emission of up to 30 degreesas measured in a direction perpendicular to the light emitting surfaceof the light conductor plate.
 2. In a surface light source device forlighting a reflective-type display device having a light source and alight conductor plate for spreading the light introduced from the lightsource to nearly entire of a light emitting surface and emitting it fromthe light emitting surface, the surface light source devicecharacterized in that: 50% or more of the light emitted from the lightconductor plate to the reflective-type display device is emitted to anarea defined by angles of within the half-width of a reflection lightintensity-angle distribution on the reflective-type display device asmeasured in a direction perpendicular to the light emitting surface ofthe light conductor plate.
 3. In a surface light source device having alight source and a light conductor plate nearly in a rectangular formfor spreading the light introduced from the light source to nearlyentire of a light emitting surface and emitting it from the lightemitting surface, the surface light source device characterized in that:50% or more of the light emitted from the light conductor plate isemitted to an area having a brightness of a half or greater of a maximumbrightness value of the emission light, the area seen in both alonger-side direction and a shorter-side direction of the lightconductor plate has an angle width of 30 degrees to 70 degrees.
 4. In asurface light source device having a light source and a light conductorplate for spreading the light introduced from the light source to nearlyentire of a light emitting surface and emitting it from the lightemitting surface, the surface light source device characterized in that:the brightness of the light emitted from the light conductor plateperpendicularly is lower than that of the light emitted to an areaaround thereof.
 5. In a surface light source device having a lightsource and a light conductor plate for spreading the light introducedfrom the light source to nearly entire of a light emitting surface andemitting it from the light emitting surface, the surface light sourcedevice characterized in that: a direction in which emission lightbrightness is maximum in a peripheral area of the light conductor plateis inclined toward a center of the light conductor plate as compared toa direction in which emission light brightness is maximum in a centralarea of the light conductor plate.
 6. In a surface light source devicehaving a light conductor plate for spreading the introduced light tonearly entire of a light emitting surface and emitting it from the lightemitting surface, a light source smaller in size as compared to a lightincident surface of the light conductor plate, luminous flux shapingmeans for spreading the light emitted from the light source to nearlyentire of the light incident surface and emitting it, the surface lightsource device characterized in that: 50% or more of the incident lighton the light conductor plate is included in an area defined by angles of26 degrees as viewed from a direction perpendicular to the lightemitting surface of the light conductor plate.
 7. A surface light sourcedevice according to claim 6, wherein two-thirds or more of the totallight emitted from the luminous flux shaping means is emitted to an areadefined by angles of up to 40 degrees from a lengthwise direction of alight emitting surface of the luminous flux shaping means as viewed froma direction perpendicular to the light emitting surface of the lightconductor plate, the luminous flux shaping means having, at a lightemitting surface side, means to deflect the light emitted from theluminous flux shaping means to a direction perpendicular to a lightemitting surface of the luminous flux shaping means.
 8. A surface lightsource device according to claim 6, wherein the luminous flux shapingmeans is formed of a transparent material, a regular reflection platebeing provided opposed to the opposite side of the light emittingsurface.
 9. In a surface light source device having a plurality ofrelatively small light sources arranged with a spacing, means fordecreasing a directivity of the light emitted from the light sources ina direction that the light sources are arranged, and a light conductorplate for spreading the light introduced from the light sources tonearly entire of a light emitting surface and emitting it from the lightemitting surface, the surface light source device characterized in that:50% or more of the incident light on the light conductor plate isincluded in an area defined by angles of 26 degrees as viewed from adirection perpendicular to the light emitting surface of the lightconductor plate.
 10. A surface light source device according to claim 6or 9, wherein, in the area, 50% or more of the incident light on thelight conductor plate is not concentrated in an area defined by anglesof up to 10 degrees in every direction.
 11. A surface light sourcedevice according to claims 6 to 10, wherein at least one of the lightemitting surface and the opposite surface of the light conductor plateis provided with a concave-formed pattern having a deflecting slantsurface which is slanted so that a normal line directed inside of thelight conductor plate inclines to a direction that the light source isarranged, a direction of the normal line and a direction of light'straveling within the light conductor plate being in parallel as viewedin a direction perpendicular to the light emitting surface of the lightconductor plate.
 12. A surface light source device according to claim11, wherein, two-thirds or more of the total light emitted within aplane perpendicular to the light emitting surface of the light conductorplate including a light's traveling direction within the light conductorplate being emitted to an area defined by angles of up to 40 degreeswith respect to the light emitting surface of the light conductor plate,the light conductor plate having, at a light emitting surface side,means to deflect the light emitted from the light emitting surface to adirection perpendicular to the light emitting surface.
 13. A surfacelight source device according to claim 12, wherein the angle defined bya normal line direction of the deflecting slant surface and a directionperpendicular to the light emitting surface of the light conductor plateis 10 degrees or smaller, a regular reflection plate being provided onthe opposite surface of the light emitting surface of the lightconductor plate.
 14. In a surface light source device having a lightsource and a light conductor plate for spreading the light introducedfrom the light source to nearly entire of a light emitting surface andemitting it from the light emitting surface, the surface light sourcedevice characterized in that: the light conductor plate having aplurality of deflecting slant surfaces for totally reflecting lightwhich travels in the light conductor plate and emitting it from a lightemitting surface; as viewed in a direction perpendicular to the lightemitting surface of the light conductor plate, a direction of lightstraveling within the light conductor plate being aligned nearly in onedirection at each position, and a direction of the normal line of thedeflecting slant surface being distributed within an area of 30 degreesabout a direction of light's traveling; and the deflecting slant surfacein a plane including a direction of light's traveling within the lightconductor plate and perpendicular to the light emitting surface of thelight conductor plate having a section of a straight line.
 15. In asurface light source device having a light source and a light conductorplate for spreading the light introduced from the light source to nearlyentire of a light emitting surface and emitting it from the lightemitting surface, the surface light source device characterized in that:at least one of the light emitting surface of the light conductor plateand the opposite surface is provided with concave-formed patterns inplurality structured with a deflecting slant surface for totalreflection of light and a light re-incident surface for re-incidence ofthe light transmitted through the deflecting slant surface; theconcave-formed pattern having a section in a triangular groove formhaving a deflecting slant surface and a light re-incident surface, and asection nearly uniform in a direction perpendicular to a direction oflight's traveling within the light conductor plate, the deflecting slantsurface having an inclination of 45-65 degrees relative to a surfacehaving the concave-formed patterns; and as viewed in a directionperpendicular to a plane including a direction of light s travelingwithin the light conductor plate and perpendicular to the light emittingsurface of the light conductor plate, 50% or more of the light to beemitted from the light emitting surface of the light conductor platebeing included in a range of within 30 degrees as viewed from the lightemitting surface.
 16. A surface light source device according to claim 1-6, 9, 14 or 15, wherein a relatively small light source is arranged atan end on a side of a shorter side of the light conductor plate nearlyin a rectangular form, a light emitting surface of the light sourcebeing directed to a corner positioned in a diagonal direction of thelight conductor plate.
 17. In a surface light source device having alight source and a light conductor plate nearly in a rectangular formfor spreading the light introduced from the light source to nearlyentire of a light emitting surface and emitting it from the lightemitting surface, the surface light source device characterized in that:a relatively small light source is arranged at an end on a side of ashorter side of the light conductor plate, a shorter side of the lightconductor plate arranged with the light source and a longer side of thelight conductor plate positioned on a side close to the light sourcehaving parts inclining relative to the respective opposed shorter sideand longer side.
 18. In a surface light source device having a lightsource and a light conductor plate for spreading the light introducedfrom the light source to nearly entire of a light emitting surface andemitting it a light emitting surf ace, the surf ace light source devicecharacterized in that: the light source has a wavelength spectrum havinga plurality of peaks, the light conductor plate having a anti-reflectionfilm formed on the light emitting surface thereof, the anti-reflectionfilm has minimum values of reflective-index waveform dependency for aperpendicular incident light existing at a plurality of points, amaximum wavelength difference of the minimum values at the plurality ofpoints being greater than a maximum wavelength difference of a pluralityof peaks of the light source.
 19. In a surface light source devicehaving a light source and a light conductor plate for spreading thelight introduced from the light source to nearly entire of a lightemitting surface and emitting it from a light emitting surface, thesurface light source device characterized in that: a plurality ofconcave-formed patterns are formed on the opposite side of the lightemitting surface of the light conductor plate, anti-reflection filmsdifferent in reflection characteristic from each other being formed onthe light emitting surface of the light conductor plate and on anopposite surface thereto.
 20. In a surface light source device having alight source and a light conductor plate for spreading the lightintroduced from the light source to nearly entire of a light emittingsurface and emitting it from a light emitting surface, the surface lightsource device characterized in that: the light conductor plate has aplurality of concave-formed patterns formed on the opposite side of thelight emitting surface, an anti-reflection film being formed on theopposite side of the light reflection surface, the anti-reflection filmhaving a film thickness of the anti-reflection film at a boundary areabetween a planar surface not in a concave-formed pattern and theconcave-formed pattern different from a film thickness of theanti-reflection film in the planar surface.
 21. A method formanufacturing a surface light source device according to claim 11, 15,19 or 20 having a plurality of concave-formed patterns formed on theopposite side of the light reflecting surface of the light conductorplate, the manufacturing method for a surface light source devicecomprises: a process of injection-forming a larger plate than a desiredlight conductor plate; and a process of cutting off undesired part ofthe plate.
 22. A liquid crystal display unit comprising a liquid crystaldisplay panel for generating an image and a surface light source deviceaccording to any one of claims 1 to 20 for lighting the liquid crystaldisplay panel.
 23. In a cellular phone having a transceiver function,the cellular phone characterized by comprising a display sectionincluding a liquid crystal display unit according to claim
 22. 24. In aninformation terminal unit having an information processing function, theinformation terminal unit characterized by comprising a display sectionincluding a liquid crystal display unit according to claim 22.